Page faulting and selective preemption

ABSTRACT

One embodiment provides for a parallel processor comprising a processing array within the parallel processor, the processing array including multiple compute blocks, each compute block including multiple processing clusters configured for parallel operation, wherein each of the multiple compute blocks is independently preemptable. In one embodiment a preemption hint can be generated for source code during compilation to enable a compute unit to determine an efficient point for preemption.

FIELD

Embodiments relate generally to data processing and more particularly todata processing via a general-purpose graphics processing unit.

BACKGROUND OF THE DESCRIPTION

Current parallel graphics data processing includes systems and methodsdeveloped to perform specific operations on graphics data such as, forexample, linear interpolation, tessellation, rasterization, texturemapping, depth testing, etc. Traditionally, graphics processors usedfixed function computational units to process graphics data; however,more recently, portions of graphics processors have been madeprogrammable, enabling such processors to support a wider variety ofoperations for processing vertex and fragment data.

To further increase performance, graphics processors typically implementprocessing techniques such as pipelining that attempt to process, inparallel, as much graphics data as possible throughout the differentparts of the graphics pipeline. Parallel graphics processors with singleinstruction, multiple thread (SIMT) architectures are designed tomaximize the amount of parallel processing in the graphics pipeline. Inan SIMT architecture; groups of parallel threads attempt to executeprogram instructions synchronously together as often as possible toincrease processing efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentembodiments can be understood in detail, a more particular descriptionof the embodiments, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments and are therefore not to be considered limiting ofits scope.

FIG. 1 is a block diagram illustrating a computer system configured toimplement one or more aspects of the embodiments described herein;

FIG. 2A-2D illustrate parallel processor components, according to anembodiment;

FIG. 3A-3B are block diagrams of graphics multiprocessors, according toembodiments;

FIG. 4A-4F illustrate an exemplary architecture in which a plurality ofGPUs are communicatively coupled to a plurality of multi-coreprocessors;

FIG. 5 is a conceptual diagram of a graphics processing pipeline,according to an embodiment;

FIG. 6 illustrates a subsystem for executing threads within asingle-instruction multiple-data (SIMD) computation system, according toan embodiment;

FIG. 7 is a block diagram for an execution subsystem within a processingarray of a GPGPU, according to an embodiment;

FIG. 8A-8B are a flow diagrams of logic to perform fine grained contextswitching, according to an embodiment;

FIG. 9 illustrates an instruction execution system according to anembodiment;

FIG. 10 illustrates an exemplary graph of hints and associated registerfile usage per thread;

FIG. 11 is a flow diagram of preemption within a compute unit, accordingto an embodiment;

FIG. 12 is a block diagram of a data processing system, according to anembodiment.

FIG. 13 is a block diagram of a processing system, according to anembodiment;

FIG. 14 is a block diagram of a processor according to an embodiment;

FIG. 15 is a block diagram of a graphics processor, according to anembodiment;

FIG. 16 is a block diagram of a graphics processing engine of a graphicsprocessor in accordance with some embodiments;

FIG. 17 is a block diagram of a graphics processor provided by anadditional embodiment;

FIG. 18 illustrates thread execution logic including an array ofprocessing elements employed in some embodiments;

FIG. 19 is a block diagram illustrating a graphics processor instructionformats according to some embodiments;

FIG. 20 is a block diagram of a graphics processor according to anotherembodiment;

FIG. 21A-21B illustrate a graphics processor command format and commandsequence, according to some embodiments;

FIG. 22 illustrates exemplary graphics software architecture for a dataprocessing system according to some embodiments;

FIG. 23 is a block diagram illustrating an IP core development system,according to an embodiment;

FIG. 24 is a block diagram illustrating an exemplary system on a chipintegrated circuit, according to an embodiment;

FIG. 25 is a block diagram illustrating an additional graphicsprocessor, according to an embodiment; and

FIG. 26 is a block diagram illustrating an additional exemplary graphicsprocessor of a system on a chip integrated circuit, according to anembodiment.

DETAILED DESCRIPTION

In some embodiments, a graphics processing unit (GPU) is communicativelycoupled to host/processor cores to accelerate graphics operations,machine-learning operations, pattern analysis operations, and variousgeneral purpose GPU (GPGPU) functions. The GPU may be communicativelycoupled to the host processor/cores over a bus or another interconnect(e.g., a high-speed interconnect such as PCIe or NVLink). In otherembodiments, the GPU may be integrated on the same package or chip asthe cores and communicatively coupled to the cores over an internalprocessor bus/interconnect (i.e., internal to the package or chip).Regardless of the manner in which the GPU is connected, the processorcores may allocate work to the GPU in the form of sequences ofcommands/instructions contained in a work descriptor. The GPU then usesdedicated circuitry/logic for efficiently processing thesecommands/instructions.

A page fault can occur on a GPGPU in response to an instruction'sattempt to access an invalid virtual address or a virtual address thatis not mapped to a physical address. For example, GPU oversubscriptioncan be implemented in which a virtual address space addressable by theGPU includes GPU local memory as well as system memory associated withhost processors of a host data processing system. When accessing avirtual address that is not currently mapped to a physical memoryaddress a page fault can occur to load the page into the relevantvirtual address space. This may include simply mapping a virtual addressto a region of local physical memory or can include an additionaloperation to loading the page from system memory into a local physicalmemory address. The page fault invokes a page fault handler thatestablishes the proper virtual to physical mapping and either resumesexecution of the faulting instruction or signals an error if the addressis invalid.

If servicing the page fault will cause significant delay the GPU mayswitch contexts to a context associated with another process or thread.The context switch results in state information being stored until thestate information is needed in response to a subsequent context switch.Performing a full GPU context switch can be significantly timeconsuming, however. The entire hardware content is saved and restoredand various hardware caches are flushed to prepare to execute a separatecontext. This process can result tin a significant loss of time from thecompute perspective. Additionally, the page fault handling process forthe context may require tracking. For example, if a context is switchedout to handle a page fault, switching the context back onto the GPUbefore the page fault is handled can introduce additional delay andhamper computational efficiency.

Embodiments described herein increase the computational efficiencyassociated with context switching by enabling a GPU to performpreemption as a lower granularity than the entire GPU. In one embodimentthe parallel execution blocks of the GPU are divided into compute blocksthat define a preemption boundary for hardware resources within the GPU.Upon a page fault affecting a compute block, hardware tracking theexecution progress of the compute blocks stops execution and place thecompute block into a preemption state. While in the preemption state thehardware context of the compute block is saved to a region in memorythat is designated for use by the compute block. While the compute blockis in the preemption state, other compute blocks on the GPU can continueto execute instructions. Once the hardware context of the compute blockis saved to memory, scheduling hardware for the GPU can load a newworkgroup onto the compute block. The work group can be from the samecontext or, in embodiments in which the GPU supports multiplesimultaneous contexts, the scheduler can load a work group for analternative context onto the preempted compute block.

As an additional optimization, in one embodiment the scheduler hardwareof the GPU can track the execution state of active workgroups for agiven context. When all workgroups of the context are complete exceptingthe page faulted and pre-empted work groups associated with the context,the scheduler hardware can preempt compute blocks associated with otheractive contexts on the GPU and reload the previously faulted andpreempted context to complete the final outstanding work groups of thatcontext. The reload process is particularly efficient for embodiments inwhich the GPU is configured to execute multiple contexts simultaneously.

In the following description, numerous specific details are set forth toprovide a more thorough understanding. However, it will be apparent toone of skill in the art that the embodiments described herein may bepracticed without one or more of these specific details. In otherinstances, well-known features have not been described to avoidobscuring the details of the present embodiments.

System Overview

FIG. 1 is a block diagram illustrating a computing system 100 configuredto implement one or more aspects of the embodiments described herein.The computing system 100 includes a processing subsystem 101 having oneor more processor(s) 102 and a system memory 104 communicating via aninterconnection path that may include a memory hub 105. The memory hub105 may be a separate component within a chipset component or may beintegrated within the one or more processor(s) 102. The memory hub 105couples with an I/O subsystem 111 via a communication link 106. The I/Osubsystem 111 includes an I/O hub 107 that can enable the computingsystem 100 to receive input from one or more input device(s) 108.Additionally, the I/O hub 107 can enable a display controller, which maybe included in the one or more processor(s) 102, to provide outputs toone or more display device(s) 110A. In one embodiment the one or moredisplay device(s) 110A coupled with the I/O hub 107 can include a local,internal, or embedded display device.

In one embodiment the processing subsystem 101 includes one or moreparallel processor(s) 112 coupled to memory hub 105 via a bus or othercommunication link 113. The communication link 113 may be one of anynumber of standards based communication link technologies or protocols,such as, but not limited to PCI Express, or may be a vendor specificcommunications interface or communications fabric. In one embodiment theone or more parallel processor(s) 112 form a computationally focusedparallel or vector processing system that can include a large number ofprocessing cores and/or processing clusters, such as a many integratedcore (MIC) processor. In one embodiment the one or more parallelprocessor(s) 112 form a graphics processing subsystem that can outputpixels to one of the one or more display device(s) 110A coupled via theI/O Hub 107. The one or more parallel processor(s) 112 can also includea display controller and display interface (not shown) to enable adirect connection to one or more display device(s) 110B.

Within the I/O subsystem 111, a system storage unit 114 can connect tothe I/O hub 107 to provide a storage mechanism for the computing system100. An I/O switch 116 can be used to provide an interface mechanism toenable connections between the I/O hub 107 and other components, such asa network adapter 118 and/or wireless network adapter 119 that may beintegrated into the platform, and various other devices that can beadded via one or more add-in device(s) 120. The network adapter 118 canbe an Ethernet adapter or another wired network adapter. The wirelessnetwork adapter 119 can include one or more of a Wi-Fi, Bluetooth, nearfield communication (NFC), or other network device that includes one ormore wireless radios.

The computing system 100 can include other components not explicitlyshown, including USB or other port connections, optical storage drives,video capture devices, and the like, may also be connected to the I/Ohub 107. Communication paths interconnecting the various components inFIG. 1 may be implemented using any suitable protocols, such as PCI(Peripheral Component Interconnect) based protocols (e.g., PCI-Express),or any other bus or point-to-point communication interfaces and/orprotocol(s), such as the NV-Link high-speed interconnect, orinterconnect protocols known in the art.

In one embodiment, the one or more parallel processor(s) 112 incorporatecircuitry optimized for graphics and video processing, including, forexample, video output circuitry, and constitutes a graphics processingunit (GPU). In another embodiment, the one or more parallel processor(s)112 incorporate circuitry optimized for general purpose processing,while preserving the underlying computational architecture, described ingreater detail herein. In yet another embodiment, components of thecomputing system 100 may be integrated with one or more other systemelements on a single integrated circuit. For example, the one or moreparallel processor(s) 112, memory hub 105, processor(s) 102, and I/O hub107 can be integrated into a system on chip (SoC) integrated circuit.Alternatively, the components of the computing system 100 can beintegrated into a single package to form a system in package (SIP)configuration. In one embodiment at least a portion of the components ofthe computing system 100 can be integrated into a multi-chip module(MCM), which can be interconnected with other multi-chip modules into amodular computing system.

It will be appreciated that the computing system 100 shown herein isillustrative and that variations and modifications are possible. Theconnection topology, including the number and arrangement of bridges,the number of processor(s) 102, and the number of parallel processor(s)112, may be modified as desired. For instance, in some embodiments,system memory 104 is connected to the processor(s) 102 directly ratherthan through a bridge, while other devices communicate with systemmemory 104 via the memory hub 105 and the processor(s) 102. In otheralternative topologies, the parallel processor(s) 112 are connected tothe I/O hub 107 or directly to one of the one or more processor(s) 102,rather than to the memory hub 105. In other embodiments, the I/O hub 107and memory hub 105 may be integrated into a single chip. Someembodiments may include two or more sets of processor(s) 102 attachedvia multiple sockets, which can couple with two or more instances of theparallel processor(s) 112.

Some of the particular components shown herein are optional and may notbe included in all implementations of the computing system 100. Forexample, any number of add-in cards or peripherals may be supported, orsome components may be eliminated.

FIG. 2A illustrates a parallel processor 200, according to anembodiment. The various components of the parallel processor 200 may beimplemented using one or more integrated circuit devices, such asprogrammable processors, application specific integrated circuits(ASICs), or field programmable gate arrays (FPGA). The illustratedparallel processor 200 is a variant of the one or more parallelprocessor(s) 112 shown in FIG. 1, according to an embodiment.

In one embodiment the parallel processor 200 includes a parallelprocessing unit 202. The parallel processing unit includes an I/O unit204 that enables communication with other devices, including otherinstances of the parallel processing unit 202. The I/O unit 204 may bedirectly connected to other devices. In one embodiment the I/O unit 204connects with other devices via the use of a hub or switch interface,such as memory hub 105. The connections between the memory hub 105 andthe I/O unit 204 form a communication link 113. Within the parallelprocessing unit 202, the I/O unit 204 connects with a host interface 206and a memory crossbar 216, where the host interface 206 receivescommands directed to performing processing operations and the memorycrossbar 216 receives commands directed to performing memory operations.

When the host interface 206 receives a command buffer via the I/O unit204, the host interface 206 can direct work operations to perform thosecommands to a front end 208. In one embodiment the front end 208 coupleswith a scheduler 210, which is configured to distribute commands orother work items to a processing cluster array 212. In one embodimentthe scheduler 210 ensures that the processing cluster array 212 isproperly configured and in a valid state before tasks are distributed tothe processing clusters of the processing cluster array 212.

The processing cluster array 212 can include up to “N” processingclusters (e.g., cluster 214A, cluster 214B, through cluster 214N). Eachcluster 214A-214N of the processing cluster array 212 can execute alarge number of concurrent threads. The scheduler 210 can allocate workto the clusters 214A-214N of the processing cluster array 212 usingvarious scheduling and/or work distribution algorithms, which may varydepending on the workload arising for each type of program orcomputation. The scheduling can be handled dynamically by the scheduler210, or can be assisted in part by compiler logic during compilation ofprogram logic configured for execution by the processing cluster array212. In one embodiment, different clusters 214A-214N of the processingcluster array 212 can be allocated for processing different types ofprograms or for performing different types of computations.

The processing cluster array 212 can be configured to perform varioustypes of parallel processing operations. In one embodiment theprocessing cluster array 212 is configured to perform general-purposeparallel compute operations. For example, the processing cluster array212 can include logic to execute processing tasks including filtering ofvideo and/or audio data, performing modeling operations, includingphysics operations, and performing data transformations.

In one embodiment the processing cluster array 212 is configured toperform parallel graphics processing operations. In embodiments in whichthe parallel processor 200 is configured to perform graphics processingoperations, the processing cluster array 212 can include additionallogic to support the execution of such graphics processing operations,including, but not limited to texture sampling logic to perform textureoperations, as well as tessellation logic and other vertex processinglogic. Additionally, the processing cluster array 212 can be configuredto execute graphics processing related shader programs such as, but notlimited to vertex shaders, tessellation shaders, geometry shaders, andpixel shaders. The parallel processing unit 202 can transfer data fromsystem memory via the I/O unit 204 for processing. During processing thetransferred data can be stored to on-chip memory (e.g., parallelprocessor memory 222) during processing, then written back to systemmemory.

In one embodiment, when the parallel processing unit 202 is used toperform graphics processing, the scheduler 210 can be configured todivide the processing workload into approximately equal sized tasks, tobetter enable distribution of the graphics processing operations tomultiple clusters 214A-214N of the processing cluster array 212. In someembodiments, portions of the processing cluster array 212 can beconfigured to perform different types of processing. For example a firstportion may be configured to perform vertex shading and topologygeneration, a second portion may be configured to perform tessellationand geometry shading, and a third portion may be configured to performpixel shading or other screen space operations, to produce a renderedimage for display. Intermediate data produced by one or more of theclusters 214A-214N may be stored in buffers to allow the intermediatedata to be transmitted between clusters 214A-214N for furtherprocessing.

During operation, the processing cluster array 212 can receiveprocessing tasks to be executed via the scheduler 210, which receivescommands defining processing tasks from front end 208. For graphicsprocessing operations, processing tasks can include indices of data tobe processed, e.g., surface (patch) data, primitive data, vertex data,and/or pixel data, as well as state parameters and commands defining howthe data is to be processed (e.g., what program is to be executed). Thescheduler 210 may be configured to fetch the indices corresponding tothe tasks or may receive the indices from the front end 208. The frontend 208 can be configured to ensure the processing cluster array 212 isconfigured to a valid state before the workload specified by incomingcommand buffers (e.g., batch-buffers, push buffers, etc.) is initiated.

Each of the one or more instances of the parallel processing unit 202can couple with parallel processor memory 222. The parallel processormemory 222 can be accessed via the memory crossbar 216, which canreceive memory requests from the processing cluster array 212 as well asthe I/O unit 204. The memory crossbar 216 can access the parallelprocessor memory 222 via a memory interface 218. The memory interface218 can include multiple partition units (e.g., partition unit 220A,partition unit 220B, through partition unit 220N) that can each coupleto a portion (e.g., memory unit) of parallel processor memory 222. Inone implementation the number of partition units 220A-220N is configuredto be equal to the number of memory units, such that a first partitionunit 220A has a corresponding first memory unit 224A, a second partitionunit 220B has a corresponding memory unit 224B, and an Nth partitionunit 220N has a corresponding Nth memory unit 224N. In otherembodiments, the number of partition units 220A-220N may not be equal tothe number of memory devices.

In various embodiments, the memory units 224A-224N can include varioustypes of memory devices, including dynamic random access memory (DRAM)or graphics random access memory, such as synchronous graphics randomaccess memory (SGRAM), including graphics double data rate (GDDR)memory. In one embodiment, the memory units 224A-224N may also include3D stacked memory, including but not limited to high bandwidth memory(HBM). Persons skilled in the art will appreciate that the specificimplementation of the memory units 224A-224N can vary, and can beselected from one of various conventional designs. Render targets, suchas frame buffers or texture maps may be stored across the memory units224A-224N, allowing partition units 220A-220N to write portions of eachrender target in parallel to efficiently use the available bandwidth ofparallel processor memory 222. In some embodiments, a local instance ofthe parallel processor memory 222 may be excluded in favor of a unifiedmemory design that utilizes system memory in conjunction with localcache memory.

In one embodiment, any one of the clusters 214A-214N of the processingcluster array 212 can process data that will be written to any of thememory units 224A-224N within parallel processor memory 222. The memorycrossbar 216 can be configured to transfer the output of each cluster214A-214N to any partition unit 220A-220N or to another cluster214A-214N, which can perform additional processing operations on theoutput. Each cluster 214A-214N can communicate with the memory interface218 through the memory crossbar 216 to read from or write to variousexternal memory devices. In one embodiment the memory crossbar 216 has aconnection to the memory interface 218 to communicate with the I/O unit204, as well as a connection to a local instance of the parallelprocessor memory 222, enabling the processing units within the differentprocessing clusters 214A-214N to communicate with system memory or othermemory that is not local to the parallel processing unit 202. In oneembodiment the memory crossbar 216 can use virtual channels to separatetraffic streams between the clusters 214A-214N and the partition units220A-220N.

While a single instance of the parallel processing unit 202 isillustrated within the parallel processor 200, any number of instancesof the parallel processing unit 202 can be included. For example,multiple instances of the parallel processing unit 202 can be providedon a single add-in card, or multiple add-in cards can be interconnected.The different instances of the parallel processing unit 202 can beconfigured to inter-operate even if the different instances havedifferent numbers of processing cores, different amounts of localparallel processor memory, and/or other configuration differences. Forexample and in one embodiment, some instances of the parallel processingunit 202 can include higher precision floating point units relative toother instances. Systems incorporating one or more instances of theparallel processing unit 202 or the parallel processor 200 can beimplemented in a variety of configurations and form factors, includingbut not limited to desktop, laptop, or handheld personal computers,servers, workstations, game consoles, and/or embedded systems.

FIG. 2B is a block diagram of a partition unit 220, according to anembodiment. In one embodiment the partition unit 220 is an instance ofone of the partition units 220A-220N of FIG. 2A. As illustrated, thepartition unit 220 includes an L2 cache 221, a frame buffer interface225, and a ROP 226 (raster operations unit). The L2 cache 221 is aread/write cache that is configured to perform load and store operationsreceived from the memory crossbar 216 and ROP 226. Read misses andurgent write-back requests are output by L2 cache 221 to frame bufferinterface 225 for processing. Updates can also be sent to the framebuffer via the frame buffer interface 225 for processing. In oneembodiment the frame buffer interface 225 interfaces with one of thememory units in parallel processor memory, such as the memory units224A-224N of FIG. 2A (e.g., within parallel processor memory 222).

In graphics applications, the ROP 226 is a processing unit that performsraster operations such as stencil, z test, blending, and the like. TheROP 226 then outputs processed graphics data that is stored in graphicsmemory. In some embodiments the ROP 226 includes compression logic tocompress depth or color data that is written to memory and decompressdepth or color data that is read from memory. In some embodiments, theROP 226 is included within each processing cluster (e.g., cluster214A-214N of FIG. 2A) instead of within the partition unit 220. In suchembodiment, read and write requests for pixel data are transmitted overthe memory crossbar 216 instead of pixel fragment data. The processedgraphics data may be displayed on a display device, such as one of theone or more display device(s) 110 of FIG. 1, routed for furtherprocessing by the processor(s) 102, or routed for further processing byone of the processing entities within the parallel processor 200 of FIG.2A.

FIG. 2C is a block diagram of a processing cluster 214 within a parallelprocessing unit, according to an embodiment. In one embodiment theprocessing cluster is an instance of one of the processing clusters214A-214N of FIG. 2A. The processing cluster 214 can be configured toexecute many threads in parallel, where the term “thread” refers to aninstance of a particular program executing on a particular set of inputdata. In some embodiments, single-instruction, multiple-data (SIMD)instruction issue techniques are used to support parallel execution of alarge number of threads without providing multiple independentinstruction units. In other embodiments, single-instruction,multiple-thread (SIMT) techniques are used to support parallel executionof a large number of generally synchronized threads, using a commoninstruction unit configured to issue instructions to a set of processingengines within each one of the processing clusters. Unlike a SIMDexecution regime, where all processing engines typically executeidentical instructions, SIMT execution allows different threads to morereadily follow divergent execution paths through a given thread program.Persons skilled in the art will understand that a SIMD processing regimerepresents a functional subset of a SIMT processing regime.

Operation of the processing cluster 214 can be controlled via a pipelinemanager 232 that distributes processing tasks to SIMT parallelprocessors. The pipeline manager 232 receives instructions from thescheduler 210 of FIG. 2A and manages execution of those instructions viaa graphics multiprocessor 234 and/or a texture unit 236. The illustratedgraphics multiprocessor 234 is an exemplary instance of a SIMT parallelprocessor. However, various types of SIMT parallel processors ofdiffering architectures may be included within the processing cluster214. One or more instances of the graphics multiprocessor 234 can beincluded within a processing cluster 214. The graphics multiprocessor234 can process data and a data crossbar 240 can be used to distributethe processed data to one of multiple possible destinations, includingother shader units. The pipeline manager 232 can facilitate thedistribution of processed data by specifying destinations for processeddata to be distributed via the data crossbar 240.

Each graphics multiprocessor 234 within the processing cluster 214 caninclude an identical set of functional execution logic (e.g., arithmeticlogic units, load-store units, etc.). The functional execution logic canbe configured in a pipelined manner in which new instructions can beissued before previous instructions are complete. The functionalexecution logic supports a variety of operations including integer andfloating point arithmetic, comparison operations, Boolean operations,bit-shifting, and computation of various algebraic functions. In oneembodiment the same functional-unit hardware can be leveraged to performdifferent operations and any combination of functional units may bepresent.

The instructions transmitted to the processing cluster 214 constitutes athread. A set of threads executing across the set of parallel processingengines is a thread group. A thread group executes the same program ondifferent input data. Each thread within a thread group can be assignedto a different processing engine within a graphics multiprocessor 234. Athread group may include fewer threads than the number of processingengines within the graphics multiprocessor 234. When a thread groupincludes fewer threads than the number of processing engines, one ormore of the processing engines may be idle during cycles in which thatthread group is being processed. A thread group may also include morethreads than the number of processing engines within the graphicsmultiprocessor 234. When the thread group includes more threads than thenumber of processing engines within the graphics multiprocessor 234,processing can be performed over consecutive clock cycles. In oneembodiment multiple thread groups can be executed concurrently on agraphics multiprocessor 234.

In one embodiment the graphics multiprocessor 234 includes an internalcache memory to perform load and store operations. In one embodiment,the graphics multiprocessor 234 can forego an internal cache and use acache memory (e.g., L1 cache 248) within the processing cluster 214.Each graphics multiprocessor 234 also has access to L2 caches within thepartition units (e.g., partition units 220A-220N of FIG. 2A) that areshared among all processing clusters 214 and may be used to transferdata between threads. The graphics multiprocessor 234 may also accessoff-chip global memory, which can include one or more of local parallelprocessor memory and/or system memory. Any memory external to theparallel processing unit 202 may be used as global memory. Embodimentsin which the processing cluster 214 includes multiple instances of thegraphics multiprocessor 234 can share common instructions and data,which may be stored in the L1 cache 248.

Each processing cluster 214 may include an MMU 245 (memory managementunit) that is configured to map virtual addresses into physicaladdresses. In other embodiments, one or more instances of the MMU 245may reside within the memory interface 218 of FIG. 2A. The MMU 245includes a set of page table entries (PTEs) used to map a virtualaddress to a physical address of a tile and optionally a cache lineindex. The MMU 245 may include address translation lookaside buffers(TLB) or caches that may reside within the graphics multiprocessor 234or the L1 cache or processing cluster 214. The physical address isprocessed to distribute surface data access locality to allow efficientrequest interleaving among partition units. The cache line index may beused to determine whether a request for a cache line is a hit or miss.

In graphics and computing applications, a processing cluster 214 may beconfigured such that each graphics multiprocessor 234 is coupled to atexture unit 236 for performing texture mapping operations, e.g.,determining texture sample positions, reading texture data, andfiltering the texture data. Texture data is read from an internaltexture L1 cache (not shown) or in some embodiments from the L1 cachewithin graphics multiprocessor 234 and is fetched from an L2 cache,local parallel processor memory, or system memory, as needed. Eachgraphics multiprocessor 234 outputs processed tasks to the data crossbar240 to provide the processed task to another processing cluster 214 forfurther processing or to store the processed task in an L2 cache, localparallel processor memory, or system memory via the memory crossbar 216.A preROP 242 (pre-raster operations unit) is configured to receive datafrom graphics multiprocessor 234, direct data to ROP units, which may belocated with partition units as described herein (e.g., partition units220A-220N of FIG. 2A). The preROP 242 unit can perform optimizations forcolor blending, organize pixel color data, and perform addresstranslations.

It will be appreciated that the core architecture described herein isillustrative and that variations and modifications are possible. Anynumber of processing units, e.g., graphics multiprocessor 234, textureunits 236, preROPs 242, etc., may be included within a processingcluster 214. Further, while only one processing cluster 214 is shown, aparallel processing unit as described herein may include any number ofinstances of the processing cluster 214. In one embodiment, eachprocessing cluster 214 can be configured to operate independently ofother processing clusters 214 using separate and distinct processingunits, L1 caches, etc.

FIG. 2D shows a graphics multiprocessor 234, according to oneembodiment. In such embodiment the graphics multiprocessor 234 coupleswith the pipeline manager 232 of the processing cluster 214. Thegraphics multiprocessor 234 has an execution pipeline including but notlimited to an instruction cache 252, an instruction unit 254, an addressmapping unit 256, a register file 258, one or more general purposegraphics processing unit (GPGPU) cores 262, and one or more load/storeunits 266. The GPGPU cores 262 and load/store units 266 are coupled withcache memory 272 and shared memory 270 via a memory and cacheinterconnect 268.

In one embodiment, the instruction cache 252 receives a stream ofinstructions to execute from the pipeline manager 232. The instructionsare cached in the instruction cache 252 and dispatched for execution bythe instruction unit 254. The instruction unit 254 can dispatchinstructions as thread groups (e.g., warps), with each thread of thethread group assigned to a different execution unit within GPGPU core262. An instruction can access any of a local, shared, or global addressspace by specifying an address within a unified address space. Theaddress mapping unit 256 can be used to translate addresses in theunified address space into a distinct memory address that can beaccessed by the load/store units 266.

The register file 258 provides a set of registers for the functionalunits of the graphics multiprocessor 234. The register file 258 providestemporary storage for operands connected to the data paths of thefunctional units (e.g., GPGPU cores 262, load/store units 266) of thegraphics multiprocessor 234. In one embodiment, the register file 258 isdivided between each of the functional units such that each functionalunit is allocated a dedicated portion of the register file 258. In oneembodiment, the register file 258 is divided between the different warpsbeing executed by the graphics multiprocessor 234.

The GPGPU cores 262 can each include floating point units (FPUs) and/orinteger arithmetic logic units (ALUs) that are used to executeinstructions of the graphics multiprocessor 234. The GPGPU cores 262 canbe similar in architecture or can differ in architecture, according toembodiments. For example and in one embodiment, a first portion of theGPGPU cores 262 include a single precision FPU and an integer ALU whilea second portion of the GPGPU cores include a double precision FPU. Inone embodiment the FPUs can implement the IEEE 754-2008 standard forfloating point arithmetic or enable variable precision floating pointarithmetic. The graphics multiprocessor 234 can additionally include oneor more fixed function or special function units to perform specificfunctions such as copy rectangle or pixel blending operations. In oneembodiment one or more of the GPGPU cores can also include fixed orspecial function logic

The memory and cache interconnect 268 is an interconnect network thatconnects each of the functional units of the graphics multiprocessor 234to the register file 258 and to the shared memory 270. In oneembodiment, the memory and cache interconnect 268 is a crossbarinterconnect that allows the load/store unit 266 to implement load andstore operations between the shared memory 270 and the register file258. shared memory 270 can be used to enable communication betweenthreads that execute on the functional units within the graphicsmultiprocessor 234. The cache memory 272 can be used as a data cache forexample, to cache texture data communicated between the functional unitsand the texture unit 236.

FIG. 3A-3B illustrate additional graphics multiprocessors, according toembodiments. The illustrated graphics multiprocessors 325, 350 arevariants of the graphics multiprocessor 234 of FIG. 2C. The illustratedgraphics multiprocessors 325, 350 can be configured as a streamingmultiprocessor (SM) capable of simultaneous execution of a large numberof execution threads.

FIG. 3A shows a graphics multiprocessor 325 according to an additionalembodiment. The graphics multiprocessor 325 includes multiple additionalinstances of execution resource units relative to the graphicsmultiprocessor 234 of FIG. 2D. For example, the graphics multiprocessor325 can include multiple instances of the instruction unit 332A-332B,register file 334A-334B, and texture unit(s) 344A-344B. The graphicsmultiprocessor 325 also includes multiple sets of graphics or computeexecution units (e.g., GPGPU core 336A-336B, GPGPU core 337A-337B, GPGPUcore 338A-338B) and multiple sets of load/store units 340A-340B. In oneembodiment the execution resource units have a common instruction cache330, texture and/or data cache memory 342, and shared memory 346. Thevarious components can communicate via an interconnect fabric 327. Inone embodiment the interconnect fabric 327 includes one or more crossbarswitches to enable communication between the various components of thegraphics multiprocessor 325.

FIG. 3B shows a graphics multiprocessor 350 according to an additionalembodiment. The graphics processor includes multiple sets of executionresources 356A-356D, where each set of execution resource includesmultiple instruction units, register files, GPGPU cores, and load storeunits, as illustrated in FIG. 2D and FIG. 3A. The execution resources356A-356D can work in concert with texture unit(s) 360A-360D for textureoperations, while sharing an instruction cache 354, and shared memory362. In one embodiment the execution resources 356A-356D can share aninstruction cache 354 and shared memory 362, as well as multipleinstances of a texture and/or data cache memory 358A-358B. The variouscomponents can communicate via an interconnect fabric 352 similar to theinterconnect fabric 327 of FIG. 3A.

Persons skilled in the art will understand that the architecturedescribed in FIGS. 1, 2A-2D, and 3A-3B are descriptive and not limitingas to the scope of the present embodiments. Thus, the techniquesdescribed herein may be implemented on any properly configuredprocessing unit, including, without limitation, one or more mobileapplication processors, one or more desktop or server central processingunits (CPUs) including multi-core CPUs, one or more parallel processingunits, such as the parallel processing unit 202 of FIG. 2A, as well asone or more graphics processors or special purpose processing units,without departure from the scope of the embodiments described herein.

In some embodiments a parallel processor or GPGPU as described herein iscommunicatively coupled to host/processor cores to accelerate graphicsoperations, machine-learning operations, pattern analysis operations,and various general purpose GPU (GPGPU) functions. The GPU may becommunicatively coupled to the host processor/cores over a bus or otherinterconnect (e.g., a high speed interconnect such as PCIe or NVLink).In other embodiments, the GPU may be integrated on the same package orchip as the cores and communicatively coupled to the cores over aninternal processor bus/interconnect (i.e., internal to the package orchip). Regardless of the manner in which the GPU is connected, theprocessor cores may allocate work to the GPU in the form of sequences ofcommands/instructions contained in a work descriptor. The GPU then usesdedicated circuitry/logic for efficiently processing thesecommands/instructions.

Techniques for GPU to Host Processor Interconnection

FIG. 4A illustrates an exemplary architecture in which a plurality ofGPUs 410-413 are communicatively coupled to a plurality of multi-coreprocessors 405-406 over high-speed links 440A-440D (e.g., buses,point-to-point interconnects, etc.). In one embodiment, the high-speedlinks 440A-440D support a communication throughput of 4 GB/s, 30 GB/s,80 GB/s or higher, depending on the implementation. Various interconnectprotocols may be used including, but not limited to, PCIe 4.0 or 5.0 andNVLink 2.0. However, the underlying principles of the invention are notlimited to any particular communication protocol or throughput.

In addition, in one embodiment, two or more of the GPUs 410-413 areinterconnected over high-speed links 442A-442B, which may be implementedusing the same or different protocols/links than those used forhigh-speed links 440A-440D. Similarly, two or more of the multi-coreprocessors 405-406 may be connected over high speed link 443 which maybe symmetric multi-processor (SMP) buses operating at 20 GB/s, 30 GB/s,120 GB/s or higher. Alternatively, all communication between the varioussystem components shown in FIG. 4A may be accomplished using the sameprotocols/links (e.g., over a common interconnection fabric). Asmentioned, however, the underlying principles of the invention are notlimited to any particular type of interconnect technology.

In one embodiment, each multi-core processor 405-406 is communicativelycoupled to a processor memory 401-402, via memory interconnects430A-430B, respectively, and each GPU 410-413 is communicatively coupledto GPU memory 420-423 over GPU memory interconnects 450A-450D,respectively. The memory interconnects 430A-430B and 450A-450D mayutilize the same or different memory access technologies. By way ofexample, and not limitation, the processor memories 401-402 and GPUmemories 420-423 may be volatile memories such as dynamic random accessmemories (DRAMs) (including stacked DRAMs), Graphics DDR SDRAM (GDDR)(e.g., GDDR5, GDDR6), or High Bandwidth Memory (HBM) and/or may benon-volatile memories such as 3D XPoint or Nano-Ram. In one embodiment,some portion of the memories may be volatile memory and another portionmay be non-volatile memory (e.g., using a two-level memory (2LM)hierarchy).

As described below, although the various processors 405-406 and GPUs410-413 may be physically coupled to a particular memory 401-402,420-423, respectively, a unified memory architecture may be implementedin which the same virtual system address space (also referred to as the“effective address” space) is distributed among all of the variousphysical memories. For example, processor memories 401-402 may eachcomprise 64 GB of the system memory address space and GPU memories420-423 may each comprise 32 GB of the system memory address space(resulting in a total of 256 GB addressable memory in this example).

FIG. 4B illustrates additional details for an interconnection between amulti-core processor 407 and a graphics acceleration module 446 inaccordance with one embodiment. The graphics acceleration module 446 mayinclude one or more GPU chips integrated on a line card which is coupledto the processor 407 via the high-speed link 440. Alternatively, thegraphics acceleration module 446 may be integrated on the same packageor chip as the processor 407.

The illustrated processor 407 includes a plurality of cores 460A-460D,each with a translation lookaside buffer 461A-461D and one or morecaches 462A-462D. The cores may include various other components forexecuting instructions and processing data which are not illustrated toavoid obscuring the underlying principles of the invention (e.g.,instruction fetch units, branch prediction units, decoders, executionunits, reorder buffers, etc.). The caches 462A-462D may comprise level 1(L1) and level 2 (L2) caches. In addition, one or more shared caches 456may be included in the caching hierarchy and shared by sets of the cores460A-460D. For example, one embodiment of the processor 407 includes 24cores, each with its own L1 cache, twelve shared L2 caches, and twelveshared L3 caches. In this embodiment, one of the L2 and L3 caches areshared by two adjacent cores. The processor 407 and the graphicsaccelerator integration module 446 connect with system memory 441, whichmay include processor memories 401-402.

Coherency is maintained for data and instructions stored in the variouscaches 462A-462D, 456 and system memory 441 via inter-core communicationover a coherence bus 464. For example, each cache may have cachecoherency logic/circuitry associated therewith to communicate to overthe coherence bus 464 in response to detected reads or writes toparticular cache lines. In one implementation, a cache snooping protocolis implemented over the coherence bus 464 to snoop cache accesses. Cachesnooping/coherency techniques are well understood by those of skill inthe art and will not be described in detail here to avoid obscuring theunderlying principles of the invention.

In one embodiment, a proxy circuit 425 communicatively couples thegraphics acceleration module 446 to the coherence bus 464, allowing thegraphics acceleration module 446 to participate in the cache coherenceprotocol as a peer of the cores. In particular, an interface 435provides connectivity to the proxy circuit 425 over high-speed link 440(e.g., a PCIe bus, NVLink, etc.) and an interface 437 connects thegraphics acceleration module 446 to the high-speed link 440.

In one implementation, an accelerator integration circuit 436 providescache management, memory access, context management, and interruptmanagement services on behalf of a plurality of graphics processingengines 431, 432, N of the graphics acceleration module 446. Thegraphics processing engines 431, 432, N may each comprise a separategraphics processing unit (GPU). Alternatively, the graphics processingengines 431, 432, N may comprise different types of graphics processingengines within a GPU such as graphics execution units, media processingengines (e.g., video encoders/decoders), samplers, and blit engines. Inother words, the graphics acceleration module may be a GPU with aplurality of graphics processing engines 431-432, N or the graphicsprocessing engines 431-432, N may be individual GPUs integrated on acommon package, line card, or chip.

In one embodiment, the accelerator integration circuit 436 includes amemory management unit (MMU) 439 for performing various memorymanagement functions such as virtual-to-physical memory translations(also referred to as effective-to-real memory translations) and memoryaccess protocols for accessing system memory 441. The MMU 439 may alsoinclude a translation lookaside buffer (TLB) (not shown) for caching thevirtual/effective to physical/real address translations. In oneimplementation, a cache 438 stores commands and data for efficientaccess by the graphics processing engines 431-432, N. In one embodiment,the data stored in cache 438 and graphics memories 433-434, M is keptcoherent with the core caches 462A-462D, 456 and system memory 411. Asmentioned, this may be accomplished via proxy circuit 425 which takespart in the cache coherency mechanism on behalf of cache 438 andmemories 433-434, M (e.g., sending updates to the cache 438 related tomodifications/accesses of cache lines on processor caches 462A-462D, 456and receiving updates from the cache 438).

A set of registers 445 store context data for threads executed by thegraphics processing engines 431-432, N and a context management circuit448 manages the thread contexts. For example, the context managementcircuit 448 may perform save and restore operations to save and restorecontexts of the various threads during contexts switches (e.g., where afirst thread is saved and a second thread is stored so that the secondthread can be execute by a graphics processing engine). For example, ona context switch, the context management circuit 448 may store currentregister values to a designated region in memory (e.g., identified by acontext pointer). It may then restore the register values when returningto the context. In one embodiment, an interrupt management circuit 447receives and processes interrupts received from system devices.

In one implementation, virtual/effective addresses from a graphicsprocessing engine 431 are translated to real/physical addresses insystem memory 411 by the MMU 439. One embodiment of the acceleratorintegration circuit 436 supports multiple (e.g., 4, 8, 16) graphicsaccelerator modules 446 and/or other accelerator devices. The graphicsaccelerator module 446 may be dedicated to a single application executedon the processor 407 or may be shared between multiple applications. Inone embodiment, a virtualized graphics execution environment ispresented in which the resources of the graphics processing engines431-432, N are shared with multiple applications or virtual machines(VMs). The resources may be subdivided into “slices” which are allocatedto different VMs and/or applications based on the processingrequirements and priorities associated with the VMs and/or applications.

Thus, the accelerator integration circuit acts as a bridge to the systemfor the graphics acceleration module 446 and provides addresstranslation and system memory cache services. In addition, theaccelerator integration circuit 436 may provide virtualizationfacilities for the host processor to manage virtualization of thegraphics processing engines, interrupts, and memory management.

Because hardware resources of the graphics processing engines 431-432, Nare mapped explicitly to the real address space seen by the hostprocessor 407, any host processor can address these resources directlyusing an effective address value. One function of the acceleratorintegration circuit 436, in one embodiment, is the physical separationof the graphics processing engines 431-432, N so that they appear to thesystem as independent units.

As mentioned, in the illustrated embodiment, one or more graphicsmemories 433-434, M are coupled to each of the graphics processingengines 431-432, N, respectively. The graphics memories 433-434, M storeinstructions and data being processed by each of the graphics processingengines 431-432, N. The graphics memories 433-434, M may be volatilememories such as DRAMs (including stacked DRAMs), GDDR memory (e.g.,GDDR5, GDDR6), or HBM, and/or may be non-volatile memories such as 3DXPoint or Nano-Ram.

In one embodiment, to reduce data traffic over the high-speed link 440,biasing techniques are used to ensure that the data stored in graphicsmemories 433-434, M is data which will be used most frequently by thegraphics processing engines 431-432, N and preferably not used by thecores 460A-460D (at least not frequently). Similarly, the biasingmechanism attempts to keep data needed by the cores (and preferably notthe graphics processing engines 431-432, N) within the caches 462A-462D,456 of the cores and system memory 411.

FIG. 4C illustrates another embodiment in which the acceleratorintegration circuit 436 is integrated within the processor 407. In thisembodiment, the graphics processing engines 431-432, N communicatedirectly over the high-speed link 440 to the accelerator integrationcircuit 436 via interface 437 and interface 435 (which, again, may beutilize any form of bus or interface protocol). The acceleratorintegration circuit 436 may perform the same operations as thosedescribed with respect to FIG. 4B, but potentially at a higherthroughput given its close proximity to the coherency bus 464 and caches462A-462D, 456.

One embodiment supports different programming models including adedicated-process programming model (no graphics acceleration modulevirtualization) and shared programming models (with virtualization). Thelatter may include programming models which are controlled by theaccelerator integration circuit 436 and programming models which arecontrolled by the graphics acceleration module 446.

In one embodiment of the dedicated process model, graphics processingengines 431-432, N are dedicated to a single application or processunder a single operating system. The single application can funnel otherapplication requests to the graphics engines 431-432, N, providingvirtualization within a VM/partition.

In the dedicated-process programming models, the graphics processingengines 431-432, N, may be shared by multiple VM/application partitions.The shared models require a system hypervisor to virtualize the graphicsprocessing engines 431-432, N to allow access by each operating system.For single-partition systems without a hypervisor, the graphicsprocessing engines 431-432, N are owned by the operating system. In bothcases, the operating system can virtualize the graphics processingengines 431-432, N to provide access to each process or application.

For the shared programming model, the graphics acceleration module 446or an individual graphics processing engine 431-432, N selects a processelement using a process handle. In one embodiment, process elements arestored in system memory 411 and are addressable using the effectiveaddress to real address translation techniques described herein. Theprocess handle may be an implementation-specific value provided to thehost process when registering its context with the graphics processingengine 431-432, N (that is, calling system software to add the processelement to the process element linked list). The lower 16-bits of theprocess handle may be the offset of the process element within theprocess element linked list.

FIG. 4D illustrates an exemplary accelerator integration slice 490. Asused herein, a “slice” comprises a specified portion of the processingresources of the accelerator integration circuit 436. Applicationeffective address space 482 within system memory 411 stores processelements 483. In one embodiment, the process elements 483 are stored inresponse to GPU invocations 481 from applications 480 executed on theprocessor 407. A process element 483 contains the process state for thecorresponding application 480. A work descriptor (WD) 484 contained inthe process element 483 can be a single job requested by an applicationor may contain a pointer to a queue of jobs. In the latter case, the WD484 is a pointer to the job request queue in the application's addressspace 482.

The graphics acceleration module 446 and/or the individual graphicsprocessing engines 431-432, N can be shared by all or a subset of theprocesses in the system. Embodiments of the invention include aninfrastructure for setting up the process state and sending a WD 484 toa graphics acceleration module 446 to start a job in a virtualizedenvironment.

In one implementation, the dedicated-process programming model isimplementation-specific. In this model, a single process owns thegraphics acceleration module 446 or an individual graphics processingengine 431. Because the graphics acceleration module 446 is owned by asingle process, the hypervisor initializes the accelerator integrationcircuit 436 for the owning partition and the operating systeminitializes the accelerator integration circuit 436 for the owningprocess at the time when the graphics acceleration module 446 isassigned.

In operation, a WD fetch unit 491 in the accelerator integration slice490 fetches the next WD 484 which includes an indication of the work tobe done by one of the graphics processing engines of the graphicsacceleration module 446. Data from the WD 484 may be stored in registers445 and used by the MMU 439, interrupt management circuit 447 and/orcontext management circuit 448 as illustrated. For example, oneembodiment of the MMU 439 includes segment/page walk circuitry foraccessing segment/page tables 486 within the OS virtual address space485. The interrupt management circuit 447 may process interrupt events492 received from the graphics acceleration module 446. When performinggraphics operations, an effective address 493 generated by a graphicsprocessing engine 431-432, N is translated to a real address by the MMU439.

In one embodiment, the same set of registers 445 are duplicated for eachgraphics processing engine 431-432, N and/or graphics accelerationmodule 446 and may be initialized by the hypervisor or operating system.Each of these duplicated registers may be included in an acceleratorintegration slice 490. Exemplary registers that may be initialized bythe hypervisor are shown in Table 1.

TABLE 1 Hypervisor Initialized Registers 1 Slice Control Register 2 RealAddress (RA) Scheduled Processes Area Pointer 3 Authority Mask OverrideRegister 4 Interrupt Vector Table Entry Offset 5 Interrupt Vector TableEntry Limit 6 State Register 7 Logical Partition ID 8 Real address (RA)Hypervisor Accelerator Utilization Record Pointer 9 Storage DescriptionRegister

Exemplary registers that may be initialized by the operating system areshown in Table 2.

TABLE 2 Operating System Initialized Registers 1 Process and ThreadIdentification 2 Effective Address (EA) Context Save/Restore Pointer 3Virtual Address (VA) Accelerator Utilization Record Pointer 4 VirtualAddress (VA) Storage Segment Table Pointer 5 Authority Mask 6 Workdescriptor

In one embodiment, each WD 484 is specific to a particular graphicsacceleration module 446 and/or graphics processing engine 431-432, N. Itcontains all the information a graphics processing engine 431-432, Nrequires to do its work or it can be a pointer to a memory locationwhere the application has set up a command queue of work to becompleted.

FIG. 4E illustrates additional details for one embodiment of a sharedmodel. This embodiment includes a hypervisor real address space 498 inwhich a process element list 499 is stored. The hypervisor real addressspace 498 is accessible via a hypervisor 496 which virtualizes thegraphics acceleration module engines for the operating system 495.

The shared programming models allow for all or a subset of processesfrom all or a subset of partitions in the system to use a graphicsacceleration module 446. There are two programming models where thegraphics acceleration module 446 is shared by multiple processes andpartitions: time-sliced shared and graphics directed shared.

In this model, the system hypervisor 496 owns the graphics accelerationmodule 446 and makes its function available to all operating systems495. For a graphics acceleration module 446 to support virtualization bythe system hypervisor 496, the graphics acceleration module 446 mayadhere to the following requirements: 1) An application's job requestmust be autonomous (that is, the state does not need to be maintainedbetween jobs), or the graphics acceleration module 446 must provide acontext save and restore mechanism. 2) An application's job request isguaranteed by the graphics acceleration module 446 to complete in aspecified amount of time, including any translation faults, or thegraphics acceleration module 446 provides the ability to preempt theprocessing of the job. 3) The graphics acceleration module 446 must beguaranteed fairness between processes when operating in the directedshared programming model.

In one embodiment, for the shared model, the application 480 is requiredto make an operating system 495 system call with a graphics accelerationmodule 446 type, a work descriptor (WD), an authority mask register(AMR) value, and a context save/restore area pointer (CSRP). Thegraphics acceleration module 446 type describes the targetedacceleration function for the system call. The graphics accelerationmodule 446 type may be a system-specific value. The WD is formattedspecifically for the graphics acceleration module 446 and can be in theform of a graphics acceleration module 446 command, an effective addresspointer to a user-defined structure, an effective address pointer to aqueue of commands, or any other data structure to describe the work tobe done by the graphics acceleration module 446. In one embodiment, theAMR value is the AMR state to use for the current process. The valuepassed to the operating system is similar to an application setting theAMR. If the accelerator integration circuit 436 and graphicsacceleration module 446 implementations do not support a User AuthorityMask Override Register (UAMOR), the operating system may apply thecurrent UAMOR value to the AMR value before passing the AMR in thehypervisor call. The hypervisor 496 may optionally apply the currentAuthority Mask Override Register (AMOR) value before placing the AMRinto the process element 483. In one embodiment, the CSRP is one of theregisters 445 containing the effective address of an area in theapplication's address space 482 for the graphics acceleration module 446to save and restore the context state. This pointer is optional if nostate is required to be saved between jobs or when a job is preempted.The context save/restore area may be pinned system memory.

Upon receiving the system call, the operating system 495 may verify thatthe application 480 has registered and been given the authority to usethe graphics acceleration module 446. The operating system 495 thencalls the hypervisor 496 with the information shown in Table 3.

TABLE 3 OS to Hypervisor Call Parameters 1 A work descriptor (WD) 2 AnAuthority Mask Register (AMR) value (potentially masked). 3 An effectiveaddress (EA) Context Save/Restore Area Pointer (CSRP) 4 A process ID(PID) and optional thread ID (TID) 5 A virtual address (VA) acceleratorutilization record pointer (AURP) 6 The virtual address of the storagesegment table pointer (SSTP) 7 A logical interrupt service number (LISN)

Upon receiving the hypervisor call, the hypervisor 496 verifies that theoperating system 495 has registered and been given the authority to usethe graphics acceleration module 446. The hypervisor 496 then puts theprocess element 483 into the process element linked list for thecorresponding graphics acceleration module 446 type. The process elementmay include the information shown in Table 4.

TABLE 4 Process Element Information 1 A work descriptor (WD) 2 AnAuthority Mask Register (AMR) value (potentially masked). 3 An effectiveaddress (EA) Context Save/Restore Area Pointer (CSRP) 4 A process ID(PID) and optional thread ID (TID) 5 A virtual address (VA) acceleratorutilization record pointer (AURP) 6 The virtual address of the storagesegment table pointer (SSTP) 7 A logical interrupt service number (LISN)8 Interrupt vector table, derived from the hypervisor call parameters. 9A state register (SR) value 10 A logical partition ID (LPID) 11 A realaddress (RA) hypervisor accelerator utilization record pointer 12 TheStorage Descriptor Register (SDR)

In one embodiment, the hypervisor initializes a plurality of acceleratorintegration slice 490 registers 445.

As illustrated in FIG. 4F, one embodiment of the invention employs aunified memory addressable via a common virtual memory address spaceused to access the physical processor memories 401-402 and GPU memories420-423. In this implementation, operations executed on the GPUs 410-413utilize the same virtual/effective memory address space to access theprocessors memories 401-402 and vice versa, thereby simplifyingprogrammability. In one embodiment, a first portion of thevirtual/effective address space is allocated to the processor memory401, a second portion to the second processor memory 402, a thirdportion to the GPU memory 420, and so on. The entire virtual/effectivememory space (sometimes referred to as the effective address space) isthereby distributed across each of the processor memories 401-402 andGPU memories 420-423, allowing any processor or GPU to access anyphysical memory with a virtual address mapped to that memory.

In one embodiment, bias/coherence management circuitry 494A-494E withinone or more of the MMUs 439A-439E ensures cache coherence between thecaches of the host processors (e.g., 405) and the GPUs 410-413 andimplements biasing techniques indicating the physical memories in whichcertain types of data should be stored. While multiple instances ofbias/coherence management circuitry 494A-494E are illustrated in FIG.4F, the bias/coherence circuitry may be implemented within the MMU ofone or more host processors 405 and/or within the acceleratorintegration circuit 436.

One embodiment allows GPU-attached memory 420-423 to be mapped as partof system memory, and accessed using shared virtual memory (SVM)technology, but without suffering the typical performance drawbacksassociated with full system cache coherence. The ability to GPU-attachedmemory 420-423 to be accessed as system memory without onerous cachecoherence overhead provides a beneficial operating environment for GPUoffload. This arrangement allows the host processor 405 software tosetup operands and access computation results, without the overhead oftradition I/O DMA data copies. Such traditional copies involve drivercalls, interrupts and memory mapped I/O (MMIO) accesses that are allinefficient relative to simple memory accesses. At the same time, theability to access GPU attached memory 420-423 without cache coherenceoverheads can be critical to the execution time of an offloadedcomputation. In cases with substantial streaming write memory traffic,for example, cache coherence overhead can significantly reduce theeffective write bandwidth seen by a GPU 410-413. The efficiency ofoperand setup, the efficiency of results access, and the efficiency ofGPU computation all play a role in determining the effectiveness of GPUoffload.

In one implementation, the selection of between GPU bias and hostprocessor bias is driven by a bias tracker data structure. A bias tablemay be used, for example, which may be a page-granular structure (i.e.,controlled at the granularity of a memory page) that includes 1 or 2bits per GPU-attached memory page. The bias table may be implemented ina stolen memory range of one or more GPU-attached memories 420-423, withor without a bias cache in the GPU 410-413 (e.g., to cachefrequently/recently used entries of the bias table). Alternatively, theentire bias table may be maintained within the GPU.

In one implementation, the bias table entry associated with each accessto the GPU-attached memory 420-423 is accessed prior the actual accessto the GPU memory, causing the following operations. First, localrequests from the GPU 410-413 that find their page in GPU bias areforwarded directly to a corresponding GPU memory 420-423. Local requestsfrom the GPU that find their page in host bias are forwarded to theprocessor 405 (e.g., over a high-speed link as discussed above). In oneembodiment, requests from the processor 405 that find the requested pagein host processor bias complete the request like a normal memory read.Alternatively, requests directed to a GPU-biased page may be forwardedto the GPU 410-413. The GPU may then transition the page to a hostprocessor bias if it is not currently using the page.

The bias state of a page can be changed either by a software-basedmechanism, a hardware-assisted software-based mechanism, or, for alimited set of cases, a purely hardware-based mechanism.

One mechanism for changing the bias state employs an API call (e.g.OpenCL), which, in turn, calls the GPU's device driver which, in turn,sends a message (or enqueues a command descriptor) to the GPU directingit to change the bias state and, for some transitions, perform a cacheflushing operation in the host. The cache flushing operation is requiredfor a transition from host processor 405 bias to GPU bias, but is notrequired for the opposite transition.

In one embodiment, cache coherency is maintained by temporarilyrendering GPU-biased pages uncacheable by the host processor 405. Toaccess these pages, the processor 405 may request access from the GPU410 which may or may not grant access right away, depending on theimplementation. Thus, to reduce communication between the processor 405and GPU 410 it is beneficial to ensure that GPU-biased pages are thosewhich are required by the GPU but not the host processor 405 and viceversa.

Graphics Processing Pipeline

FIG. 5 illustrates a graphics processing pipeline 500, according to anembodiment. In one embodiment a graphics processor can implement theillustrated graphics processing pipeline 500. The graphics processor canbe included within the parallel processing subsystems as describedherein, such as the parallel processor 200 of FIG. 2A, which, in oneembodiment, is a variant of the parallel processor(s) 112 of FIG. 1. Thevarious parallel processing systems can implement the graphicsprocessing pipeline 500 via one or more instances of the parallelprocessing unit (e.g., parallel processing unit 202 of FIG. 2A) asdescribed herein. For example, a shader unit (e.g., graphicsmultiprocessor 234 of FIG. 2C) may be configured to perform thefunctions of one or more of a vertex processing unit 504, a tessellationcontrol processing unit 508, a tessellation evaluation processing unit512, a geometry processing unit 516, and a fragment/pixel processingunit 524. The functions of data assembler 502, primitive assemblers 506,514, 518, tessellation unit 510, rasterizer 522, and raster operationsunit 526 may also be performed by other processing engines within aprocessing cluster (e.g., processing cluster 214 of FIG. 2A) and acorresponding partition unit (e.g., partition unit 220A-220N of FIG.2A). The graphics processing pipeline 500 may also be implemented usingdedicated processing units for one or more functions. In one embodiment,one or more portions of the graphics processing pipeline 500 can beperformed by parallel processing logic within a general purposeprocessor (e.g., CPU). In one embodiment, one or more portions of thegraphics processing pipeline 500 can access on-chip memory (e.g.,parallel processor memory 222 as in FIG. 2A) via a memory interface 528,which may be an instance of the memory interface 218 of FIG. 2A.

In one embodiment the data assembler 502 is a processing unit thatcollects vertex data for surfaces and primitives. The data assembler 502then outputs the vertex data, including the vertex attributes, to thevertex processing unit 504. The vertex processing unit 504 is aprogrammable execution unit that executes vertex shader programs,lighting and transforming vertex data as specified by the vertex shaderprograms. The vertex processing unit 504 reads data that is stored incache, local or system memory for use in processing the vertex data andmay be programmed to transform the vertex data from an object-basedcoordinate representation to a world space coordinate space or anormalized device coordinate space.

A first instance of a primitive assembler 506 receives vertex attributesfrom the vertex processing unit 504. The primitive assembler 506readings stored vertex attributes as needed and constructs graphicsprimitives for processing by tessellation control processing unit 508.The graphics primitives include triangles, line segments, points,patches, and so forth, as supported by various graphics processingapplication programming interfaces (APIs).

The tessellation control processing unit 508 treats the input verticesas control points for a geometric patch. The control points aretransformed from an input representation from the patch (e.g., thepatch's bases) to a representation that is suitable for use in surfaceevaluation by the tessellation evaluation processing unit 512. Thetessellation control processing unit 508 can also compute tessellationfactors for edges of geometric patches. A tessellation factor applies toa single edge and quantifies a view-dependent level of detail associatedwith the edge. A tessellation unit 510 is configured to receive thetessellation factors for edges of a patch and to tessellate the patchinto multiple geometric primitives such as line, triangle, orquadrilateral primitives, which are transmitted to a tessellationevaluation processing unit 512. The tessellation evaluation processingunit 512 operates on parameterized coordinates of the subdivided patchto generate a surface representation and vertex attributes for eachvertex associated with the geometric primitives.

A second instance of a primitive assembler 514 receives vertexattributes from the tessellation evaluation processing unit 512, readingstored vertex attributes as needed, and constructs graphics primitivesfor processing by the geometry processing unit 516. The geometryprocessing unit 516 is a programmable execution unit that executesgeometry shader programs to transform graphics primitives received fromprimitive assembler 514 as specified by the geometry shader programs. Inone embodiment the geometry processing unit 516 is programmed tosubdivide the graphics primitives into one or more new graphicsprimitives and calculate parameters used to rasterize the new graphicsprimitives.

In some embodiments the geometry processing unit 516 can add or deleteelements in the geometry stream. The geometry processing unit 516outputs the parameters and vertices specifying new graphics primitivesto primitive assembler 518. The primitive assembler 518 receives theparameters and vertices from the geometry processing unit 516 andconstructs graphics primitives for processing by a viewport scale, cull,and clip unit 520. The geometry processing unit 516 reads data that isstored in parallel processor memory or system memory for use inprocessing the geometry data. The viewport scale, cull, and clip unit520 performs clipping, culling, and viewport scaling and outputsprocessed graphics primitives to a rasterizer 522.

The rasterizer 522 can perform depth culling and other depth-basedoptimizations. The rasterizer 522 also performs scan conversion on thenew graphics primitives to generate fragments and output those fragmentsand associated coverage data to the fragment/pixel processing unit 524.The fragment/pixel processing unit 524 is a programmable execution unitthat is configured to execute fragment shader programs or pixel shaderprograms. The fragment/pixel processing unit 524 transforming fragmentsor pixels received from rasterizer 522, as specified by the fragment orpixel shader programs. For example, the fragment/pixel processing unit524 may be programmed to perform operations included but not limited totexture mapping, shading, blending, texture correction and perspectivecorrection to produce shaded fragments or pixels that are output to araster operations unit 526. The fragment/pixel processing unit 524 canread data that is stored in either the parallel processor memory or thesystem memory for use when processing the fragment data. Fragment orpixel shader programs may be configured to shade at sample, pixel, tile,or other granularities depending on the sampling rate configured for theprocessing units.

The raster operations unit 526 is a processing unit that performs rasteroperations including, but not limited to stencil, z test, blending, andthe like, and outputs pixel data as processed graphics data to be storedin graphics memory (e.g., parallel processor memory 222 as in FIG. 2A,and/or system memory 104 as in FIG. 1), to be displayed on the one ormore display device(s) 110 or for further processing by one of the oneor more processor(s) 102 or parallel processor(s) 112. In someembodiments the raster operations unit 526 is configured to compress zor color data that is written to memory and decompress z or color datathat is read from memory.

Page Faulting Preemption at Lower Level Hierarchy

FIG. 6 illustrates a subsystem 600 for executing threads within asingle-instruction multiple-data (SIMD) computation system, according toan embodiment. The subsystem 600 includes a front end 608, a scheduler610, and a processing array 612, which, in one embodiment, arerespective instances of the front end 208, scheduler 210, and processingarray 212 shown in FIG. 2A. In such embodiment, the front end is incommunication with a host interface, such as the host interface 206 ofFIG. 2A. The processing array 612 includes processing clusters614A-614H, which can each be an instance of the processing cluster 214of FIG. 2A and FIG. 2C.

In one embodiment the processing clusters 614A-614H are grouped intocompute blocks 620A-620B. For example, processing cluster 614A-614D canbe grouped into compute block 620A, while processing cluster 614E-614Hcan be grouped into compute block 620B. However, the illustratedgrouping of processing clusters and compute blocks is exemplary, as anynumber of compute blocks and processing clusters can be included in theprocessing array 612. The compute blocks 620A-620B are configured aspreemption group, such that the processing clusters within any givencompute block can be context switched without impacting the execution ofprocessing clusters in a different compute block. For example, if athread executing on any of processing clusters 614A-614D within computeblock 620A triggers a page fault or incurs any other form of memoryaccess related execution delay, the current state for the work groupassociated with the thread can be saved and a new work group can beloaded onto the compute block 620A without impacting the execution ofwork groups executing on compute block 620B.

The processing clusters 614A-614H of the compute blocks 620A-620B canexecute a large number of threads in parallel while utilizing a set ofshared assets 618. The shared assets 618 can include hardware resourcessuch as texture units, texture samplers, and cache memories. The sharedassets 618 can additional include address generation units and addressmapping units to enable the processing clusters 614A-614H to accesslocal memory and system. During thread execution various state andcontext information for the shared assets 618 is generated.Additionally, each of the processing clusters 614A-614H can haveassociated internal state that is generated or modified duringinstruction execution. When a context switch is triggered for any of thecompute blocks 620A-620B, the context information for the internal stateof the processing clusters within the compute block as well as thecontext state associated with the portion of the shared assets 618accessed by the compute block, can be saved and execution can be haltedonly for the affected compute block.

FIG. 7 is a block diagram for an execution subsystem 700 within aprocessing array of a GPGPU, according to an embodiment. The executionsubsystem 700 enables fine grain preemption within a GPGPU by allowingindividual portions of the GPGPU to be context switched while otherportions of the GPGPU continue to execute. Additionally, in someembodiments the GPGPU supports execution of multiple simultaneouscontexts, enabling multiple applications to simultaneously rendergraphics data or perform general purpose computational operations.Additionally the GPGPU may be configured to perform simultaneousexecution of graphics and compute instructions.

In some embodiments the execution subsystem 700 includes an embeddedmicrocontroller (e.g., scheduler micro-controller 710) configured toexecute firmware logic to perform scheduling operations for computeblock 620A-620N. The firmware of the scheduler micro-controller 710 canenable complex scheduling behavior for at least a portion of the GPGPU.In one embodiment the scheduler micro-controller 710 is configured toschedule and manage the execution of work items and work groups withinthe execution subsystem 700. In various embodiments the work items andwork groups executed can include threads, thread groups, thread blocks,thread warps, cooperative thread arrays, or any other grouping orarrangement of instructions. During execution, the various executionresources within each compute block 620A-620N can make use of sharedassets 618, as described in FIG. 6. The work groups and associated workitems can be scheduled at various degrees of granularity acrossembodiments. The degree of granularity can vary, for example, based onthe number of execution resources (e.g., processing clusters, graphicsmultiprocessors, etc.) associated with each compute block 620A-620N. Inother words, while the compute blocks 620A-620N can define thepreemption boundaries at which execution resources may be preempted,depending on the specific embodiment the compute block 620A-620N may notdefine the scheduling granularity at which the schedulermicro-controller 710 can dispatch work items for execution.

During execution, one or more thread executing on the compute blocks620A-620N can encounter page faults. In one embodiment once the numberof page faults within a compute block exceeds a threshold the computeblock is transitioned into a preemption ready state. In one embodimentthe page fault threshold is defined as a percentage of the number ofthreads executing on a compute block. For example and in one embodiment,the threshold is defined as one third of the threads executing on thecompute block. In one embodiment the threshold is defined as one half ofthe threads executing on the compute block. However, the specificthreshold value can vary across embodiments. In one embodiment the pagefault threshold is configurable.

Execution of threads for the execution resources (processing clusters,graphics multiprocessors, etc.) is halted and the context state for thework group executing on the compute block is saved. Once the executionresources within the compute block terminate execution the context statefor the executing work group can be saved to memory. In one embodimentthe scheduler micro-controller 710 can copy the state information tocontext data 722A-722N regions in a context save memory that is reservedfor each of the respective compute blocks 620A-620N. The context data722A-722N regions can store internal state for the execution resourceswithin each compute block 620A-620N, as well as the context data for theportion of the shared assets 618 used by the compute blocks to executework groups. In one embodiment the execution subsystem 700 supportsexecution of multiple simultaneous contexts. For example, compute block620A can execute rendering or compute operations for a first applicationwhile compute block 620B can execute rendering or compute operations fora second application. The number of supported active contexts can varyacross embodiments.

Under some circumstances, overly aggressive preemption may result in areduction, rather than an increase in overall system performance. Ifpreemption is performed to satisfy a page fault that is quicklyresolved, execution efficiency may be reduced. Rapid page faultresolution may occur, for example, when servicing a soft page fault. Asoft page fault occurs when a page has temporarily been unmapped fromvirtual memory but the data in memory is still valid. Such page faultsmay be satisfied by simply remapping the page to the appropriate virtualmemory address. Soft page faults differ from hard page faults, for whicha memory transfer is required.

In one embodiment the scheduler micro-controller 710 is configured toavoid overly aggressive preemption by monitoring average page faultlatency on a per-context basis. The average page fault latency for acontext can then be compared against a low-watermark threshold and ahigh-watermark threshold. When the scheduler micro-controller 710detects that average page fault latency for a context is below thelow-watermark threshold, the scheduler will disable page fault basedwork group or thread preemption from that context. When the schedulermicro-controller 710 detects that average page fault latency for acontext is above the high-watermark threshold, the scheduler can enablepage fault preemption for that context. In one embodiment the GPGPU canbe configured with a default low-watermark threshold value andhigh-watermark threshold value. The low and high-watermark thresholdvalues can also be adjusted via configuration software or by driverlogic within software executing on a host processor. In one embodimentthe watermark threshold values can be stored within hardware registerswithin the GPGPU. In one embodiment the driver logic can store watermarkthreshold values within memory.

FIG. 8A is a flow diagram of execution resource logic 800 to performfine grained context switching, according to an embodiment. In oneembodiment the execution resource logic 800 can be performed byscheduler logic within a GPGPU. In one embodiment the scheduler logiccan be implemented by a micro-controller within the GPGPU, such as thescheduler micro-controller 710 of FIG. 7. However, embodiments are notlimited to micro-controller based scheduling implementations.

As shown at 802, the execution resource logic 800 can receive a noticethat a number of page faults at one of multiple compute blocks within aGPGPU have exceeded a threshold. In one embodiment the executionresource logic 800 can receive the notice from the compute block. In oneembodiment the execution resource logic 800 monitors the execution stateof the execution resources within the multiple compute blocks and takesnotice of any execution blocking events associated with those executionresources. The specific value of the threshold associated with thenumber of page faults can vary across embodiments. In one embodiment apage fault threshold is predefined within hardware. In one embodiment apage fault threshold is dynamically configured based on the number ofwork items and/or work groups that are pending execution.

As shown at 804, the execution resource logic 800 can save the hardwarecontext of the faulted compute block to context memory associated withthe compute block. The saved hardware context includes all hardwarestate information for the execution resources within the compute block,as well as any context associated with shared assets used by the computeblock, that is necessary to subsequently resume execution of thesoon-to-be preempted work group. The precise hardware state that issaved depends on the underlying microarchitecture of the computeresources within the compute blocks and varies across embodiments.

As shown at 805, the execution resource logic 800 can then determine ifthere are any work groups pending for the same context that waspreviously being executed. If any work groups for the current samecontext are pending, the execution resource logic 800 can load thepending work group on the compute block at 810. In one embodiment theGPGPU associated with the execution resource logic 800 supportsexecution of multiple simultaneous contexts. In such embodiment, if nowork groups are pending for the same context at 805, the executionresource logic 800 can determine if work groups are pending for adifferent context at 807. If no additional work group are pending, theexecution resource logic 800 can wait until additional work is ready tobe scheduled for the same context at 805 or a different context at 807.If any work groups are pending for a different context at 807, theexecution resource logic 800 can configure the compute block to executethe different context at 808, before loading the pending work group onthe compute block at 810.

In one embodiment the illustrated operations additionally include anoptimization in which contexts having a nearly completed set ofworkgroups can be given preemption priority. For example, when allworkgroups of the context are complete excepting page faulted andpreviously preempted work groups the scheduler hardware can preemptcompute blocks associated with other active contexts on the GPGPU tofree execution resources to reload the previously faulted and preemptedcontext. Such optimization may enable more efficient usage of GPGPUresources by allowing nearly completed work to retire and releaseassociated resources.

FIG. 8B is a flow diagram of scheduler logic 820 to enable or disablefine grained context switching, according to an embodiment. In oneembodiment the scheduler logic 820 is implemented within a scheduler,such as the scheduler micro-controller 710 of FIG. 7. The schedulerlogic 820 can read the configured watermark threshold for the GPGPU, asshown at block 802. The configured watermark thresholds include alow-watermark threshold and a high-watermark threshold. In oneembodiment the thresholds are read from a hardware register within theGPGPU. In one embodiment the thresholds are supplied by driver logic forthe GPGPU. While the thresholds are configurable, one embodiment enablesthe thresholds to be pre-configured to default values. The schedulerlogic 820 can read the average page fault latency of a context, as shownat block 804. If the average page fault latency is below thelow-watermark threshold at block 805, the scheduler logic 820 candisable page fault preemption for the context at block 810. If theaverage page fault latency is above the low-watermark threshold at block805, the scheduler logic 820 can determine if the average latency isabove the high-watermark threshold at block 807. If the average latencyis above the high-watermark threshold at block 807, the scheduler logic820 can enable page fault preemption for the context at block 808.

Selective Preemption Based on Commands or Instruction Type

A GPGPU can have a large number of cores that can support a simultaneousexecution of hundreds or thousands of threads. For example, currentproductized generations can run about 100 threads simultaneously. AGPGPU that supports instruction level preemption when running computeworkloads can stop execution at an instruction boundary and save threadstate into memory. Depending on the number of resources in use at thetime of preemption, a large amount of thread state may be required to bestored to enable instruction level preemption. The amount of threadstate that is required to be saved and restored also increases inrelation to the total number of supported threads on the GPGPU. In someGPGPU implementations when a preemption request is received theexecution resources stop executing, wait for outstanding operations tocomplete, and saves the current thread state. However, scenarios canoccur in which if the execution resources continued to execute a fewadditional instructions the number of registers in use would besignificantly reduced, resulting in a smaller amount of state data to besaved and restored.

In embodiments described herein, a compiler that compiles source codefor execution on a GPGPU can generate hints to the GPGPU instructionresources as to potential upcoming changes in the amount of activethread state. The compiler hints, in one embodiment, can indicate therelative efficiency of performing preemption at a given instruction,including whether the instruction is an optimal point to stop executionand save state. The compiler hint can also indicate to the executionresources whether it would be beneficial to continue executing a fewadditional instructions to reach a more optimal state for preemption.When a preemption request is received for a work group (e.g., threadgroup, thread block, warp, etc.), on a per thread basis the computehardware can either stop execution immediately or execute a fewadditional instructions to reduce the register file footprint.

FIG. 9 illustrates an instruction execution system 900 according to anembodiment. In one embodiment the instruction execution system 900 isconfigured to process metadata 902 and an associated instruction 904 viaa compute unit 920. In one embodiment the compute unit 920 is structuredin a similar manner as the graphics multiprocessor 400 of FIG. 4.However, the compute unit 920 can be any of the instruction levelexecution units described herein. The compute unit 920 can include afetch unit 922 to fetch instruction to execute and a decode unit 924 todecode the fetched instructions. The compute unit 920 additionallyincludes execution resources 928 having one or more single precisionfloating point units, double precision floating point units, integerarithmetic logic units, load/store unit, and/or special function units.The metadata 902 and instruction 904 can be generated by a compilerexecuting on a data processing system. In one embodiment the compilergenerates the metadata based on register file usage and other threadstate data determined during the compilation process from human readablesource code to intermediate language or assembly language that canprocessed by the GPGPU.

The compute unit 920 can couple with a scheduler 910, which can bescheduler logic within a micro-controller, such as the schedulermicro-controller 710 of FIG. 7. However, embodiments are not limited tomicro-controller based schedulers. The scheduler 910 can schedule one ormore work groups to the compute unit 920 and can preempt one or more ofthe executing work groups on the compute unit 920. The scheduler 910 canpreempt work groups executing on the compute unit 920 for a variety ofreasons. For example, compute workloads on the compute unit 920 can bepreempted to maintain balance between compute and graphics renderingoperations. Additionally, the scheduler 910 can preempt work groupsexecuting on the compute unit 920 to maintain high utilization, forexample, if the number of page faults for threads executing on thecompute unit 920 exceeds a threshold.

During operation the fetch unit 922 can fetch the metadata 902 andinstruction 904 from an instruction cache. The compute decode unit 924can then decode the metadata 902 and instruction 904 to determine one ormore operations to perform based on the instruction. Decoding themetadata 902 includes parsing a preemption hint for the instruction anddetermining a status to set to a preemption status register 926 within aregister file of the compute unit 920. In one embodiment the preemptionstatus register is a single bit register that stores an OK/NOK value(e.g., 1b/0b). The decode unit 924 can decode the metadata 902associated with an instruction and set a value in the preemption statusregister 926 based on the preemption hint. In one embodiment the decodelogic can simply store the metadata 902 within the preemption statusregister 926. In such embodiment the compute unit 920 includes logic todetermine a response to a preemption request based on the value storedin the preemption status register 926. The response can be determinedbased on the preemption hint as well as other factors, including powerand performance metrics for the compute unit 920 and/or the GPGPU as awhole.

In one embodiment, the scheduler 910 can preempt a work group on thecompute unit 920 by sending a preemption request to the compute unit920. In one embodiment the scheduler 910 can interrupt the compute unit920 and indicate a work group executing on the compute unit 920 that isto be preempted. The compute unit 920, in handling the interrupt, canhalt execution immediately or continue executing additional instructionsto reduce the amount of register data, or other thread state, that issaved to preempt the work group.

While the metadata 902 is illustrated as distinct from the instruction904, in one embodiment the metadata 902 is a field within theinstruction that is parsed by the decode unit 924 while decoding theinstruction. In one embodiment, not all instructions have associatedmetadata 902. Instead the compiler can insert the metadata 902 into thecompiled code at periodic intervals or where significant changes to thesize of thread context information occurs. In one embodiment themetadata 902 is conveyed via a separate instruction that explicitly setsa value of the preemption status register 926.

The amount of data that can be encoded by a preemption hint within themetadata can be determined based on the number of bits allocated to thehint. In one embodiment a single bit may be encoded that indicateswhether preemption is optimal for a given instruction. In one embodimentmultiple bits may be encoded to give a variety of data. For example, a2-bit hint can provide information as indicated in Table 1 below.

TABLE 1 Exemplary Preemption Hint Hint (bits) Meaning 00b OptimalPreemption Point - Register File Usage Low 01b Register File Usage toIncrease Rapidly 10b Register File Usage High but Will Decrease Rapidly11b Register File Usage High with No Immediate Decrease

As shown in Table 1, a 2-bit hint can encode four values that canindicate one of four possible preemption hints associated with aninstruction. The exemplary hints are determined based on the currentper-thread register usage. For example, the hint can indicate that agiven instruction represents an optimal preemption point (e.g., 00b), asregister file usage is currently low. The compute unit 920 wouldimmediately halt execution and preempt if a preemption request werereceived while executing this instruction. The hint can also indicatethat register file usage is to increase rapidly over the next set ofinstructions (e.g., 01b). Such hint would also cause the compute unit920 to halt execution to prevent an increase in register file usage. Thehint can also indicate that register file usage is high but willdecrease rapidly over the next few instructions (e.g., 10b). In responseto a preemption request received while executing an instruction havingsuch hint, the compute unit 920 would continue executing instructionsuntil an optimal preemption point is reached. The hint an also indicatethat register file usage is high with no immediate decrease. In suchscenario the compute unit 920 can response differently depending on thedesired preemption latency. If low latency preemption is desired thecompute unit 920 can halt execution without regard to the relativelylarger amount of context that is required to be saved to performpreemption. However, if context storage space is at a premium, forexample, for GPGPUs capable of executing an extremely large number ofconcurrent threads, the compute unit 920 may continue executinginstructions until register file usage decreases. In such scenario, atimeout value can be enforced that limits the number of instructionsthat may be executed after a preemption request has been received.

FIG. 10 illustrates an exemplary graph of hints and associated registerfile usage per thread. The illustrated graph shows a relationshipbetween register file usage, as determined by a source code compiler,and the associated hints associated with the compiled instructions. Theexemplary hint values correspond to the hint values of Table 1, althoughnot all embodiments are limited to those specific hint values. In theillustrated graph, the compiler inserts preemption hints at relativepoints along the execution path to indicate whether changes are upcomingfor the the per-thread register file usage. The behavior of a computeunit can vary based on desired preemption latency and tolerance forlarge context states during preemption. In one embodiments if apreemption trigger is received (1002) while the preemption hint valueindicates that register file usage will decrease rapidly, a compute unitcan continue to execute until an optimal preemption point is reached(1004). At other points the compute unit can be configured to haltexecution immediately as reduction in register file usage (andassociated context state) is imminent. Alternatively, if register fileusage is high and context storage space is low, the compute unit cancontinue to execute until an optimal preemption point or a preemptiontimeout is reached.

FIG. 11 is a flow diagram of preemption within a compute unit, accordingto an embodiment. The preemption can be performed by hardware withincompute unit, such as the compute unit 920 of FIG. 9. In one embodimenta fetch unit within the compute unit can fetch an instruction forexecution, as shown at 1102. Decode logic can then decode a preemptionhint associated with the instruction, as shown art 1104. The preemptionhint can be derived from metadata associated with the instruction. Themetadata can be an additional set of bits or an additional fieldappending to the instruction or can be set via a separate instruction.Preemption logic within the compute unit can determine at 1105 if an ‘OKto preempt’ value can be set for the compute unit. The OK to preemptvalue can be set within a preemption status register, such as thepreemption status register 926 of FIG. 9. The preemption status register926 can be a register within the register file of the compute unit orcan be specially reserved set of bits in internal memory of the computeunit 920. The OK to preempt value can alternatively be set in a set ofstate flags within the compute unit 920.

In one embodiment if the current hint value indicates that the size ofthe per-thread state is to decrease over the next set of instruction,preemption logic within the compute unit can clear the preemption bit at1108. In such embodiment, the preemption logic can set the preemptionbit at 1106 based on any other hint value. Additionally, the preemptionbit may be set by default and cleared only if continuing to executeadditional instructions will result in a nearly immediate decrease inthe size of the pre-thread state to be saved before preemption.Alternatively, if thread state storage for suspended threads is low onavailable capacity the compute unit can continue to execute instructionsif the hint indicates that the size of the thread state to be saved ishigh, even if a reduction is not imminent. Execution can continue untilan optimal preemption point is reached or a timeout occurs.

The instruction can begin execution at block 1109. During execution, apreemption request can be received at block 1109. The response to apreemption request received during execution at 1110, in one embodiment,is dependent upon the value of the preemption bit, as determined at1111. The manner in which the preemption request is received at 1110 canvary according to embodiments. In one embodiment it may be assumed thatonce a preemption request is received, the request remains active untilthe compute unit completes execution. If the preemption bit is set, thecompute unit can halt execution immediately at 1112. If the compute bitis cleared, the compute unit can continue executing instructions, asshown at 1114 until the preemption bit is cleared based on an updatedhint.

Embodiments can be configured based on variations on the operationsillustrated in FIG. 11. For example, one embodiment does not includeadditional logic to set or clear a preemption bit. Instead, a hint valueassociated with each instruction can be temporarily stored while theinstruction is executing. If a preemption request is received thecompute unit can determine whether to continue execution based directlyon the hint bits received with the instruction.

FIG. 12 is a block diagram of a data processing system 1200, accordingto an embodiment. The data processing system 1200 is a heterogeneousprocessing system having a processor 1202, unified memory 1210, and aGPGPU 1220. The processor 1202 and the GPGPU 1220 can be any of theprocessors and GPGPU/parallel processors as described herein. Theprocessor 1202 can execute instructions for a compiler 1215 stored insystem memory 1212. The compiled 1215 executes on the processor 1202 tocompile source code 1214A into compiled code 1214B. The compiled code1214B can include code that may be executed by the processor 1202 and/orcode that may be executed by the GPGPU 1220. During compilation, thecompiler 1215 can perform operations to insert metadata, including hintsas to register file usage and/or other information related to the sizeof the per-thread context information that would be saved and restoredin the event of preemption. The compiler 1215 can include theinformation necessary to perform such operations or the operations canbe performed with the assistance of a runtime library 1216. The runtimelibrary 1216 can also facilitate the compiler 1215 in the compilation ofthe source code 1214A and can also include instructions that are linkedat runtime with the compiled code 1214B to facilitate execution on theGPGPU 1220.

The unified memory 1210 represents a unified address space that may beaccessed by the processor 1202 and the GPGPU 1220. The unified memoryincludes system memory 1212 as well as GPGPU memory 1218. The GPGPUmemory 1218 includes GPGPU local memory 1228 within the GPGPU 1220 andcan also include some or all of system memory 1212. For example,compiled code 1214B stored in system memory 1212 can also be mapped intoGPGPU memory 1218 for access by the GPGPU 1220.

The GPGPU 1220 includes multiple compute blocks 1222A-1222N, which canbe instances of the compute blocks 1220A-1220N of FIG. 12 and FIG. 7.The GPGPU 1220 also includes a set of registers 1224, cache memory 1226,and a preempt module 1225 that can be shared among the compute blocks1222A-1222N. The preempt module 1225 can be configured to manage computeblock preemption as illustrated in FIG. 8 as well as selectivepreemption based on commands or instruction type as illustrated in FIG.11. The GPGPU 1220 can additionally include GPGPU local memory 1228,which is physical memory that shares a graphics card or multi-chipmodule with the GPGPU 1220.

Additional Exemplary Graphics Processing System

Details of the embodiments described above can be incorporated withingraphics processing systems and devices described below. The graphicsprocessing system and devices of FIG. 13 through FIG. 26 illustratealternative systems and graphics processing hardware that can implementany and all of the techniques described above.

Additional Exemplary Graphics Processing System Overview

FIG. 13 is a block diagram of a processing system 1300, according to anembodiment. In various embodiments the system 1300 includes one or moreprocessors 1302 and one or more graphics processors 1308, and may be asingle processor desktop system, a multiprocessor workstation system, ora server system having a large number of processors 1302 or processorcores 1307. In one embodiment, the system 1300 is a processing platformincorporated within a system-on-a-chip (SoC) integrated circuit for usein mobile, handheld, or embedded devices.

An embodiment of system 1300 can include, or be incorporated within aserver-based gaming platform, a game console, including a game and mediaconsole, a mobile gaming console, a handheld game console, or an onlinegame console. In some embodiments system 1300 is a mobile phone, smartphone, tablet computing device or mobile Internet device. Dataprocessing system 1300 can also include, couple with, or be integratedwithin a wearable device, such as a smart watch wearable device, smarteyewear device, augmented reality device, or virtual reality device. Insome embodiments, data processing system 1300 is a television or set topbox device having one or more processors 1302 and a graphical interfacegenerated by one or more graphics processors 1308.

In some embodiments, the one or more processors 1302 each include one ormore processor cores 1307 to process instructions which, when executed,perform operations for system and user software. In some embodiments,each of the one or more processor cores 1307 is configured to process aspecific instruction set 1309. In some embodiments, instruction set 1309may facilitate Complex Instruction Set Computing (CISC), ReducedInstruction Set Computing (RISC), or computing via a Very LongInstruction Word (VLIW). Multiple processor cores 1307 may each processa different instruction set 1309, which may include instructions tofacilitate the emulation of other instruction sets. Processor core 1307may also include other processing devices, such a Digital SignalProcessor (DSP).

In some embodiments, the processor 1302 includes cache memory 1304.Depending on the architecture, the processor 1302 can have a singleinternal cache or multiple levels of internal cache. In someembodiments, the cache memory is shared among various components of theprocessor 1302. In some embodiments, the processor 1302 also uses anexternal cache (e.g., a Level-3 (L3) cache or Last Level Cache (LLC))(not shown), which may be shared among processor cores 1307 using knowncache coherency techniques. A register file 1306 is additionallyincluded in processor 1302 which may include different types ofregisters for storing different types of data (e.g., integer registers,floating point registers, status registers, and an instruction pointerregister). Some registers may be general-purpose registers, while otherregisters may be specific to the design of the processor 1302.

In some embodiments, processor 1302 is coupled with a processor bus 1310to transmit communication signals such as address, data, or controlsignals between processor 1302 and other components in system 1300. Inone embodiment the system 1300 uses an exemplary ‘hub’ systemarchitecture, including a memory controller hub 1316 and an Input Output(I/O) controller hub 1330. A memory controller hub 1316 facilitatescommunication between a memory device and other components of system1300, while an I/O Controller Hub (ICH) 1330 provides connections to I/Odevices via a local I/O bus. In one embodiment, the logic of the memorycontroller hub 1316 is integrated within the processor.

Memory device 1320 can be a dynamic random access memory (DRAM) device,a static random access memory (SRAM) device, flash memory device,phase-change memory device, or some other memory device having suitableperformance to serve as process memory. In one embodiment the memorydevice 1320 can operate as system memory for the system 1300, to storedata 1322 and instructions 1321 for use when the one or more processors1302 executes an application or process. Memory controller hub 1316 alsocouples with an optional external graphics processor 1312, which maycommunicate with the one or more graphics processors 1308 in processors1302 to perform graphics and media operations.

In some embodiments, ICH 1330 enables peripherals to connect to memorydevice 1320 and processor 1302 via a high-speed I/O bus. The I/Operipherals include, but are not limited to, an audio controller 1346, afirmware interface 1328, a wireless transceiver 1326 (e.g., Wi-Fi,Bluetooth), a data storage device 1324 (e.g., hard disk drive, flashmemory, etc.), and a legacy I/O controller 1340 for coupling legacy(e.g., Personal System 2 (PS/2)) devices to the system. One or moreUniversal Serial Bus (USB) controllers 1342 connect input devices, suchas keyboard and mouse 1344 combinations. A network controller 1334 mayalso couple with ICH 1330. In some embodiments, a high-performancenetwork controller (not shown) couples with processor bus 1310. It willbe appreciated that the system 1300 shown is exemplary and not limiting,as other types of data processing systems that are differentlyconfigured may also be used. For example, the I/O controller hub 1330may be integrated within the one or more processor 1302, or the memorycontroller hub 1316 and I/O controller hub 1330 may be integrated into adiscreet external graphics processor, such as the external graphicsprocessor 1312.

FIG. 14 is a block diagram of an embodiment of a processor 1400 havingone or more processor cores 1402A-1402N, an integrated memory controller1414, and an integrated graphics processor 1408. Those elements of FIG.14 having the same reference numbers (or names) as the elements of anyother figure herein can operate or function in any manner similar tothat described elsewhere herein, but are not limited to such. Processor1400 can include additional cores up to and including additional core1402N represented by the dashed lined boxes. Each of processor cores1402A-1402N includes one or more internal cache units 1404A-1404N. Insome embodiments each processor core also has access to one or moreshared cached units 1406.

The internal cache units 1404A-1404N and shared cache units 1406represent a cache memory hierarchy within the processor 1400. The cachememory hierarchy may include at least one level of instruction and datacache within each processor core and one or more levels of sharedmid-level cache, such as a Level 2 (L2), Level 3 (L3), Level 4 (L4), orother levels of cache, where the highest level of cache before externalmemory is classified as the LLC. In some embodiments, cache coherencylogic maintains coherency between the various cache units 1406 and1404A-1404N.

In some embodiments, processor 1400 may also include a set of one ormore bus controller units 1416 and a system agent core 1410. The one ormore bus controller units 1416 manage a set of peripheral buses, such asone or more Peripheral Component Interconnect buses (e.g., PCI, PCIExpress). System agent core 1410 provides management functionality forthe various processor components. In some embodiments, system agent core1410 includes one or more integrated memory controllers 1414 to manageaccess to various external memory devices (not shown).

In some embodiments, one or more of the processor cores 1402A-1402Ninclude support for simultaneous multi-threading. In such embodiment,the system agent core 1410 includes components for coordinating andoperating cores 1402A-1402N during multi-threaded processing. Systemagent core 1410 may additionally include a power control unit (PCU),which includes logic and components to regulate the power state ofprocessor cores 1402A-1402N and graphics processor 1408.

In some embodiments, processor 1400 additionally includes graphicsprocessor 1408 to execute graphics processing operations. In someembodiments, the graphics processor 1408 couples with the set of sharedcache units 1406, and the system agent core 1410, including the one ormore integrated memory controllers 1414. In some embodiments, a displaycontroller 1411 is coupled with the graphics processor 1408 to drivegraphics processor output to one or more coupled displays. In someembodiments, display controller 1411 may be a separate module coupledwith the graphics processor via at least one interconnect, or may beintegrated within the graphics processor 1408 or system agent core 1410.

In some embodiments, a ring based interconnect unit 1412 is used tocouple the internal components of the processor 1400. However, analternative interconnect unit may be used, such as a point-to-pointinterconnect, a switched interconnect, or other techniques, includingtechniques well known in the art. In some embodiments, graphicsprocessor 1408 couples with the ring interconnect 1412 via an I/O link1413.

The exemplary I/O link 1413 represents at least one of multiplevarieties of I/O interconnects, including an on package I/O interconnectwhich facilitates communication between various processor components anda high-performance embedded memory module 1418, such as an eDRAM module.In some embodiments, each of the processor cores 1402A-1402N andgraphics processor 1408 use embedded memory modules 1418 as a sharedLast Level Cache.

In some embodiments, processor cores 1402A-1402N are homogenous coresexecuting the same instruction set architecture. In another embodiment,processor cores 1402A-1402N are heterogeneous in terms of instructionset architecture (ISA), where one or more of processor cores 1402A-1402Nexecute a first instruction set, while at least one of the other coresexecutes a subset of the first instruction set or a differentinstruction set. In one embodiment processor cores 1402A-1402N areheterogeneous in terms of microarchitecture, where one or more coreshaving a relatively higher power consumption couple with one or morepower cores having a lower power consumption. Additionally, processor1400 can be implemented on one or more chips or as an SoC integratedcircuit having the illustrated components, in addition to othercomponents.

FIG. 15 is a block diagram of a graphics processor 1500, which may be adiscrete graphics processing unit, or may be a graphics processorintegrated with a plurality of processing cores. In some embodiments,the graphics processor communicates via a memory mapped I/O interface toregisters on the graphics processor and with commands placed into theprocessor memory. In some embodiments, graphics processor 1500 includesa memory interface 1514 to access memory. Memory interface 1514 can bean interface to local memory, one or more internal caches, one or moreshared external caches, and/or to system memory.

In some embodiments, graphics processor 1500 also includes a displaycontroller 1502 to drive display output data to a display device 1520.Display controller 1502 includes hardware for one or more overlay planesfor the display and composition of multiple layers of video or userinterface elements. In some embodiments, graphics processor 1500includes a video codec engine 1506 to encode, decode, or transcode mediato, from, or between one or more media encoding formats, including, butnot limited to Moving Picture Experts Group (MPEG) formats such asMPEG-2, Advanced Video Coding (AVC) formats such as H.264/MPEG-4 AVC, aswell as the Society of Motion Picture & Television Engineers (SMPTE)421M/VC-1, and Joint Photographic Experts Group (JPEG) formats such asJPEG, and Motion JPEG (MJPEG) formats.

In some embodiments, graphics processor 1500 includes a block imagetransfer (BLIT) engine 1504 to perform two-dimensional (2D) rasterizeroperations including, for example, bit-boundary block transfers.However, in one embodiment, 2D graphics operations are performed usingone or more components of graphics processing engine (GPE) 1510. In someembodiments, GPE 1510 is a compute engine for performing graphicsoperations, including three-dimensional (3D) graphics operations andmedia operations.

In some embodiments, GPE 310 includes a 3D pipeline 1512 for performing3D operations, such as rendering three-dimensional images and scenesusing processing functions that act upon 3D primitive shapes (e.g.,rectangle, triangle, etc.). The 3D pipeline 1512 includes programmableand fixed function elements that perform various tasks within theelement and/or spawn execution threads to a 3D/Media sub-system 1515.While 3D pipeline 1512 can be used to perform media operations, anembodiment of GPE 1510 also includes a media pipeline 1516 that isspecifically used to perform media operations, such as videopost-processing and image enhancement.

In some embodiments, media pipeline 1516 includes fixed function orprogrammable logic units to perform one or more specialized mediaoperations, such as video decode acceleration, video de-interlacing, andvideo encode acceleration in place of, or on behalf of video codecengine 1506. In some embodiments, media pipeline 1516 additionallyincludes a thread spawning unit to spawn threads for execution on3D/Media sub-system 1515. The spawned threads perform computations forthe media operations on one or more graphics execution units included in3D/Media sub-system 1515.

In some embodiments, 3D/Media subsystem 1515 includes logic forexecuting threads spawned by 3D pipeline 1512 and media pipeline 1516.In one embodiment, the pipelines send thread execution requests to3D/Media subsystem 1515, which includes thread dispatch logic forarbitrating and dispatching the various requests to available threadexecution resources. The execution resources include an array ofgraphics execution units to process the 3D and media threads. In someembodiments, 3D/Media subsystem 1515 includes one or more internalcaches for thread instructions and data. In some embodiments, thesubsystem also includes shared memory, including registers andaddressable memory, to share data between threads and to store outputdata.

Exemplary Additional Graphics Processing Engine

FIG. 16 is a block diagram of a graphics processing engine 1610 of agraphics processor in accordance with some embodiments. In oneembodiment, the graphics processing engine (GPE) 1610 is a version ofthe GPE 1510 shown in FIG. 15. Elements of FIG. 16 having the samereference numbers (or names) as the elements of any other figure hereincan operate or function in any manner similar to that describedelsewhere herein, but are not limited to such. For example, the 3Dpipeline 1512 and media pipeline 1516 of FIG. 15 are illustrated. Themedia pipeline 1516 is optional in some embodiments of the GPE 1610 andmay not be explicitly included within the GPE 1610. For example and inat least one embodiment, a separate media and/or image processor iscoupled to the GPE 1610.

In some embodiments, GPE 1610 couples with or includes a commandstreamer 1603, which provides a command stream to the 3D pipeline 1512and/or media pipelines 1516. In some embodiments, command streamer 1603is coupled with memory, which can be system memory, or one or more ofinternal cache memory and shared cache memory. In some embodiments,command streamer 1603 receives commands from the memory and sends thecommands to 3D pipeline 1512 and/or media pipeline 1516. The commandsare directives fetched from a ring buffer, which stores commands for the3D pipeline 1512 and media pipeline 1516. In one embodiment, the ringbuffer can additionally include batch command buffers storing batches ofmultiple commands. The commands for the 3D pipeline 1512 can alsoinclude references to data stored in memory, such as but not limited tovertex and geometry data for the 3D pipeline 1512 and/or image data andmemory objects for the media pipeline 1516. The 3D pipeline 1512 andmedia pipeline 1516 process the commands and data by performingoperations via logic within the respective pipelines or by dispatchingone or more execution threads to a graphics core array 1614.

In various embodiments the 3D pipeline 1512 can execute one or moreshader programs, such as vertex shaders, geometry shaders, pixelshaders, fragment shaders, compute shaders, or other shader programs, byprocessing the instructions and dispatching execution threads to thegraphics core array 1614. The graphics core array 1614 provides aunified block of execution resources. Multi-purpose execution logic(e.g., execution units) within the graphic core array 1614 includessupport for various 3D API shader languages and can execute multiplesimultaneous execution threads associated with multiple shaders.

In some embodiments the graphics core array 1614 also includes executionlogic to perform media functions, such as video and/or image processing.In one embodiment, the execution units additionally includegeneral-purpose logic that is programmable to perform parallel generalpurpose computational operations, in addition to graphics processingoperations. The general purpose logic can perform processing operationsin parallel or in conjunction with general purpose logic within theprocessor core(s) 107 of FIG. 1 or core 1402A-1402N as in FIG. 14.

Output data generated by threads executing on the graphics core array1614 can output data to memory in a unified return buffer (URB) 1618.The URB 1618 can store data for multiple threads. In some embodimentsthe URB 1618 may be used to send data between different threadsexecuting on the graphics core array 1614. In some embodiments the URB1618 may additionally be used for synchronization between threads on thegraphics core array and fixed function logic within the shared functionlogic 1620.

In some embodiments, graphics core array 1614 is scalable, such that thearray includes a variable number of graphics cores, each having avariable number of execution units based on the target power andperformance level of GPE 1610. In one embodiment the execution resourcesare dynamically scalable, such that execution resources may be enabledor disabled as needed.

The graphics core array 1614 couples with shared function logic 1620that includes multiple resources that are shared between the graphicscores in the graphics core array. The shared functions within the sharedfunction logic 1620 are hardware logic units that provide specializedsupplemental functionality to the graphics core array 1614. In variousembodiments, shared function logic 1620 includes but is not limited tosampler 1621, math 1622, and inter-thread communication (ITC) 1623logic. Additionally, some embodiments implement one or more cache(s)1625 within the shared function logic 1620. A shared function isimplemented where the demand for a given specialized function isinsufficient for inclusion within the graphics core array 1614. Insteada single instantiation of that specialized function is implemented as astand-alone entity in the shared function logic 1620 and shared amongthe execution resources within the graphics core array 1614. The preciseset of functions that are shared between the graphics core array 1614and included within the graphics core array 1614 varies betweenembodiments.

FIG. 17 is a block diagram of another embodiment of a graphics processor1700. Elements of FIG. 17 having the same reference numbers (or names)as the elements of any other figure herein can operate or function inany manner similar to that described elsewhere herein, but are notlimited to such.

In some embodiments, graphics processor 1700 includes a ringinterconnect 1702, a pipeline front-end 1704, a media engine 1737, andgraphics cores 1780A-1780N. In some embodiments, ring interconnect 1702couples the graphics processor to other processing units, includingother graphics processors or one or more general-purpose processorcores. In some embodiments, the graphics processor is one of manyprocessors integrated within a multi-core processing system.

In some embodiments, graphics processor 1700 receives batches ofcommands via ring interconnect 1702. The incoming commands areinterpreted by a command streamer 1703 in the pipeline front-end 1704.In some embodiments, graphics processor 1700 includes scalable executionlogic to perform 3D geometry processing and media processing via thegraphics core(s) 1780A-1780N. For 3D geometry processing commands,command streamer 1703 supplies commands to geometry pipeline 1736. Forat least some media processing commands, command streamer 1703 suppliesthe commands to a video front-end 1734, which couples with a mediaengine 1737. In some embodiments, media engine 1737 includes a VideoQuality Engine (VQE) 1730 for video and image post-processing and amulti-format encode/decode (MFX) 1733 engine to providehardware-accelerated media data encode and decode. In some embodiments,geometry pipeline 1736 and media engine 1737 each generate executionthreads for the thread execution resources provided by at least onegraphics core 1780A.

In some embodiments, graphics processor 1700 includes scalable threadexecution resources featuring modular cores 1780A-1780N (sometimesreferred to as core slices), each having multiple sub-cores 1750A-550N,1760A-1760N (sometimes referred to as core sub-slices). In someembodiments, graphics processor 1700 can have any number of graphicscores 1780A through 1780N. In some embodiments, graphics processor 1700includes a graphics core 1780A having at least a first sub-core 1750Aand a second sub-core 1760A. In other embodiments, the graphicsprocessor is a low power processor with a single sub-core (e.g., 1750A).In some embodiments, graphics processor 1700 includes multiple graphicscores 1780A-1780N, each including a set of first sub-cores 1750A-1750Nand a set of second sub-cores 1760A-1760N. Each sub-core in the set offirst sub-cores 1750A-1750N includes at least a first set of executionunits 1752A-1752N and media/texture samplers 1754A-1754N. Each sub-corein the set of second sub-cores 1760A-1760N includes at least a secondset of execution units 1762A-1762N and samplers 1764A-1764N. In someembodiments, each sub-core 1750A-1750N, 1760A-1760N shares a set ofshared resources 1770A-1770N. In some embodiments, the shared resourcesinclude shared cache memory and pixel operation logic. Other sharedresources may also be included in the various embodiments of thegraphics processor.

Exemplary Additional Execution Units

FIG. 18 illustrates thread execution logic 1800 including an array ofprocessing elements employed in some embodiments of a GPE. Elements ofFIG. 18 having the same reference numbers (or names) as the elements ofany other figure herein can operate or function in any manner similar tothat described elsewhere herein, but are not limited to such.

In some embodiments, thread execution logic 1800 includes a shaderprocessor 1802, a thread dispatcher 1804, instruction cache 1806, ascalable execution unit array including a plurality of execution units1808A-1808N, a sampler 1810, a data cache 1812, and a data port 1814. Inone embodiment the scalable execution unit array can dynamically scaleby enabling or disabling one or more execution units (e.g., any ofexecution unit 1808A, 1808B, 1808C, 1808D, through 1808N-1 and 1808N)based on the computational requirements of a workload. In one embodimentthe included components are interconnected via an interconnect fabricthat links to each of the components. In some embodiments, threadexecution logic 1800 includes one or more connections to memory, such assystem memory or cache memory, through one or more of instruction cache1806, data port 1814, sampler 1810, and execution units 1808A-1808N. Insome embodiments, each execution unit (e.g. 1808A) is a stand-aloneprogrammable general purpose computational unit that is capable ofexecuting multiple simultaneous hardware threads while processingmultiple data elements in parallel for each thread. In variousembodiments, the array of execution units 1808A-1808N is scalable toinclude any number individual execution units.

In some embodiments, the execution units 1808A-1808N are primarily usedto execute shader programs. A shader processor 1802 can process thevarious shader programs and dispatch execution threads associated withthe shader programs via a thread dispatcher 1804. In one embodiment thethread dispatcher includes logic to arbitrate thread initiation requestsfrom the graphics and media pipelines and instantiate the requestedthreads on one or more execution unit in the execution units1808A-1808N. For example, the geometry pipeline (e.g., 1736 of FIG. 17)can dispatch vertex, tessellation, or geometry shaders to the threadexecution logic 1800 (FIG. 18) for processing. In some embodiments,thread dispatcher 1804 can also process runtime thread spawning requestsfrom the executing shader programs.

In some embodiments, the execution units 1808A-1808N support aninstruction set that includes native support for many standard 3Dgraphics shader instructions, such that shader programs from graphicslibraries (e.g., Direct 3D and OpenGL) are executed with a minimaltranslation. The execution units support vertex and geometry processing(e.g., vertex programs, geometry programs, vertex shaders), pixelprocessing (e.g., pixel shaders, fragment shaders) and general-purposeprocessing (e.g., compute and media shaders). Each of the executionunits 1808A-1808N is capable of multi-issue single instruction multipledata (SIMD) execution and multi-threaded operation enables an efficientexecution environment in the face of higher latency memory accesses.Each hardware thread within each execution unit has a dedicatedhigh-bandwidth register file and associated independent thread-state.Execution is multi-issue per clock to pipelines capable of integer,single and double precision floating point operations, SIMD branchcapability, logical operations, transcendental operations, and othermiscellaneous operations. While waiting for data from memory or one ofthe shared functions, dependency logic within the execution units1808A-1808N causes a waiting thread to sleep until the requested datahas been returned. While the waiting thread is sleeping, hardwareresources may be devoted to processing other threads. For example,during a delay associated with a vertex shader operation, an executionunit can perform operations for a pixel shader, fragment shader, oranother type of shader program, including a different vertex shader.

Each execution unit in execution units 1808A-1808N operates on arrays ofdata elements. The number of data elements is the “execution size,” orthe number of channels for the instruction. An execution channel is alogical unit of execution for data element access, masking, and flowcontrol within instructions. The number of channels may be independentof the number of physical Arithmetic Logic Units (ALUs) or FloatingPoint Units (FPUs) for a particular graphics processor. In someembodiments, execution units 1808A-1808N support integer andfloating-point data types.

The execution unit instruction set includes SIMD instructions. Thevarious data elements can be stored as a packed data type in a registerand the execution unit will process the various elements based on thedata size of the elements. For example, when operating on a 256-bit widevector, the 256 bits of the vector are stored in a register and theexecution unit operates on the vector as four separate 64-bit packeddata elements (Quad-Word (QW) size data elements), eight separate 32-bitpacked data elements (Double Word (DW) size data elements), sixteenseparate 16-bit packed data elements (Word (W) size data elements), orthirty-two separate 8-bit data elements (byte (B) size data elements).However, different vector widths and register sizes are possible.

One or more internal instruction caches (e.g., 1806) are included in thethread execution logic 1800 to cache thread instructions for theexecution units. In some embodiments, one or more data caches (e.g.,1812) are included to cache thread data during thread execution. In someembodiments, a sampler 1810 is included to provide texture sampling for3D operations and media sampling for media operations. In someembodiments, sampler 1810 includes specialized texture or media samplingfunctionality to process texture or media data during the samplingprocess before providing the sampled data to an execution unit.

During execution, the graphics and media pipelines send threadinitiation requests to thread execution logic 1800 via thread spawningand dispatch logic. Once a group of geometric objects has been processedand rasterized into pixel data, pixel processor logic (e.g., pixelshader logic, fragment shader logic, etc.) within the shader processor1802 is invoked to further compute output information and cause resultsto be written to output surfaces (e.g., color buffers, depth buffers,stencil buffers, etc.). In some embodiments, a pixel shader or fragmentshader calculates the values of the various vertex attributes that areto be interpolated across the rasterized object. In some embodiments,pixel processor logic within the shader processor 1802 then executes anapplication programming interface (API)-supplied pixel or fragmentshader program. To execute the shader program, the shader processor 1802dispatches threads to an execution unit (e.g., 1808A) via threaddispatcher 1804. In some embodiments, pixel shader 1802 uses texturesampling logic in the sampler 1810 to access texture data in texturemaps stored in memory. Arithmetic operations on the texture data and theinput geometry data compute pixel color data for each geometricfragment, or discards one or more pixels from further processing.

In some embodiments, the data port 1814 provides a memory accessmechanism for the thread execution logic 1800 output processed data tomemory for processing on a graphics processor output pipeline. In someembodiments, the data port 1814 includes or couples to one or more cachememories (e.g., data cache 1812) to cache data for memory access via thedata port.

FIG. 19 is a block diagram illustrating a graphics processor instructionformats 1900 according to some embodiments. In one or more embodiment,the graphics processor execution units support an instruction set havinginstructions in multiple formats. The solid lined boxes illustrate thecomponents that are generally included in an execution unit instruction,while the dashed lines include components that are optional or that areonly included in a sub-set of the instructions. In some embodiments,instruction format 1900 described and illustrated aremacro-instructions, in that they are instructions supplied to theexecution unit, as opposed to micro-operations resulting frominstruction decode once the instruction is processed.

In some embodiments, the graphics processor execution units nativelysupport instructions in a 128-bit instruction format 1910. A 64-bitcompacted instruction format 1930 is available for some instructionsbased on the selected instruction, instruction options, and number ofoperands. The native 128-bit instruction format 710 provides access toall instruction options, while some options and operations arerestricted in the 64-bit format 1930. The native instructions availablein the 64-bit format 1930 vary by embodiment. In some embodiments, theinstruction is compacted in part using a set of index values in an indexfield 1913. The execution unit hardware references a set of compactiontables based on the index values and uses the compaction table outputsto reconstruct a native instruction in the 128-bit instruction format1910.

For each format, instruction opcode 1912 defines the operation that theexecution unit is to perform. The execution units execute eachinstruction in parallel across the multiple data elements of eachoperand. For example, in response to an add instruction the executionunit performs a simultaneous add operation across each color channelrepresenting a texture element or picture element. By default, theexecution unit performs each instruction across all data channels of theoperands. In some embodiments, instruction control field 1914 enablescontrol over certain execution options, such as channels selection(e.g., predication) and data channel order (e.g., swizzle). Forinstructions in the 128-bit instruction format 1910 an exec-size field1916 limits the number of data channels that will be executed inparallel. In some embodiments, exec-size field 1916 is not available foruse in the 64-bit compact instruction format 1930.

Some execution unit instructions have up to three operands including twosource operands, src0 1920, src1 1922, and one destination 1918. In someembodiments, the execution units support dual destination instructions,where one of the destinations is implied. Data manipulation instructionscan have a third source operand (e.g., SRC2 1924), where the instructionopcode 1912 determines the number of source operands. An instruction'slast source operand can be an immediate (e.g., hard-coded) value passedwith the instruction.

In some embodiments, the 128-bit instruction format 1910 includes anaccess/address mode field 1926 specifying, for example, whether directregister addressing mode or indirect register addressing mode is used.When direct register addressing mode is used, the register address ofone or more operands is directly provided by bits in the instruction.

In some embodiments, the 128-bit instruction format 1910 includes anaccess/address mode field 1926, which specifies an address mode and/oran access mode for the instruction. In one embodiment the access mode isused to define a data access alignment for the instruction. Someembodiments support access modes including a 16-byte aligned access modeand a 1-byte aligned access mode, where the byte alignment of the accessmode determines the access alignment of the instruction operands. Forexample, when in a first mode, the instruction may use byte-alignedaddressing for source and destination operands and when in a secondmode, the instruction may use 16-byte-aligned addressing for all sourceand destination operands.

In one embodiment, the address mode portion of the access/address modefield 1926 determines whether the instruction is to use direct orindirect addressing. When direct register addressing mode is used bitsin the instruction directly provide the register address of one or moreoperands. When indirect register addressing mode is used, the registeraddress of one or more operands may be computed based on an addressregister value and an address immediate field in the instruction.

In some embodiments instructions are grouped based on opcode 1912bit-fields to simplify Opcode decode 1940. For an 8-bit opcode, bits 4,5, and 6 allow the execution unit to determine the type of opcode. Theprecise opcode grouping shown is merely an example. In some embodiments,a move and logic opcode group 1942 includes data movement and logicinstructions (e.g., move (mov), compare (cmp)). In some embodiments,move and logic group 1942 shares the five most significant bits (MSB),where move (mov) instructions are in the form of 0000xxxxb and logicinstructions are in the form of 0001xxxxb. A flow control instructiongroup 1944 (e.g., call, jump (jmp)) includes instructions in the form of0010xxxxb (e.g., 0x20). A miscellaneous instruction group 1946 includesa mix of instructions, including synchronization instructions (e.g.,wait, send) in the form of 0011xxxxb (e.g., 0x30). A parallel mathinstruction group 1948 includes component-wise arithmetic instructions(e.g., add, multiply (mul)) in the form of 0100xxxxb (e.g., 0x40). Theparallel math group 1948 performs the arithmetic operations in parallelacross data channels. The vector math group 1950 includes arithmeticinstructions (e.g., dp4) in the form of 0101xxxxb (e.g., 0x50). Thevector math group performs arithmetic such as dot product calculationson vector operands.

Exemplary Additional Graphics Pipeline

FIG. 20 is a block diagram of another embodiment of a graphics processor2000. Elements of FIG. 20 having the same reference numbers (or names)as the elements of any other figure herein can operate or function inany manner similar to that described elsewhere herein, but are notlimited to such.

In some embodiments, graphics processor 2000 includes a graphicspipeline 2020, a media pipeline 2030, a display engine 2040, threadexecution logic 2050, and a render output pipeline 2070. In someembodiments, graphics processor 2000 is a graphics processor within amulti-core processing system that includes one or more general purposeprocessing cores. The graphics processor is controlled by registerwrites to one or more control registers (not shown) or via commandsissued to graphics processor 2000 via a ring interconnect 2002. In someembodiments, ring interconnect 2002 couples graphics processor 2000 toother processing components, such as other graphics processors orgeneral-purpose processors. Commands from ring interconnect 2002 areinterpreted by a command streamer 2003, which supplies instructions toindividual components of graphics pipeline 2020 or media pipeline 2030.

In some embodiments, command streamer 2003 directs the operation of avertex fetcher 2005 that reads vertex data from memory and executesvertex-processing commands provided by command streamer 2003. In someembodiments, vertex fetcher 2005 provides vertex data to a vertex shader2007, which performs coordinate space transformation and lightingoperations to each vertex. In some embodiments, vertex fetcher 2005 andvertex shader 2007 execute vertex-processing instructions by dispatchingexecution threads to execution units 2052A-2052B via a thread dispatcher2031.

In some embodiments, execution units 2052A-2052B are an array of vectorprocessors having an instruction set for performing graphics and mediaoperations. In some embodiments, execution units 2052A-2052B have anattached L1 cache 2051 that is specific for each array or shared betweenthe arrays. The cache can be configured as a data cache, an instructioncache, or a single cache that is partitioned to contain data andinstructions in different partitions.

In some embodiments, graphics pipeline 2020 includes tessellationcomponents to perform hardware-accelerated tessellation of 3D objects.In some embodiments, a programmable hull shader 811 configures thetessellation operations. A programmable domain shader 817 providesback-end evaluation of tessellation output. A tessellator 2013 operatesat the direction of hull shader 2011 and contains special purpose logicto generate a set of detailed geometric objects based on a coarsegeometric model that is provided as input to graphics pipeline 2020. Insome embodiments, if tessellation is not used, tessellation components(e.g., hull shader 2011, tessellator 2013, and domain shader 2017) canbe bypassed.

In some embodiments, complete geometric objects can be processed by ageometry shader 2019 via one or more threads dispatched to executionunits 2052A-2052B, or can proceed directly to the clipper 2029. In someembodiments, the geometry shader operates on entire geometric objects,rather than vertices or patches of vertices as in previous stages of thegraphics pipeline. If the tessellation is disabled the geometry shader2019 receives input from the vertex shader 2007. In some embodiments,geometry shader 2019 is programmable by a geometry shader program toperform geometry tessellation if the tessellation units are disabled.

Before rasterization, a clipper 2029 processes vertex data. The clipper2029 may be a fixed function clipper or a programmable clipper havingclipping and geometry shader functions. In some embodiments, arasterizer and depth test component 2073 in the render output pipeline2070 dispatches pixel shaders to convert the geometric objects into perpixel representations. In some embodiments, pixel shader logic isincluded in thread execution logic 2050. In some embodiments, anapplication can bypass the rasterizer and depth test component 2073 andaccess un-rasterized vertex data via a stream out unit 2023.

The graphics processor 2000 has an interconnect bus, interconnectfabric, or some other interconnect mechanism that allows data andmessage passing amongst the major components of the processor. In someembodiments, execution units 2052A-2052B and associated cache(s) 2051,texture and media sampler 2054, and texture/sampler cache 2058interconnect via a data port 2056 to perform memory access andcommunicate with render output pipeline components of the processor. Insome embodiments, sampler 2054, caches 2051, 2058 and execution units2052A-2052B each have separate memory access paths.

In some embodiments, render output pipeline 2070 contains a rasterizerand depth test component 2073 that converts vertex-based objects into anassociated pixel-based representation. In some embodiments, therasterizer logic includes a windower/masker unit to perform fixedfunction triangle and line rasterization. An associated render cache2078 and depth cache 2079 are also available in some embodiments. Apixel operations component 2077 performs pixel-based operations on thedata, though in some instances, pixel operations associated with 2Doperations (e.g. bit block image transfers with blending) are performedby the 2D engine 2041, or substituted at display time by the displaycontroller 2043 using overlay display planes. In some embodiments, ashared L3 cache 2075 is available to all graphics components, allowingthe sharing of data without the use of main system memory.

In some embodiments, graphics processor media pipeline 2030 includes amedia engine 2037 and a video front-end 2034. In some embodiments, videofront-end 2034 receives pipeline commands from the command streamer2003. In some embodiments, media pipeline 2030 includes a separatecommand streamer. In some embodiments, video front-end 2034 processesmedia commands before sending the command to the media engine 2037. Insome embodiments, media engine 2037 includes thread spawningfunctionality to spawn threads for dispatch to thread execution logic2050 via thread dispatcher 2031.

In some embodiments, graphics processor 2000 includes a display engine2040. In some embodiments, display engine 2040 is external to processor2000 and couples with the graphics processor via the ring interconnect2002, or some other interconnect bus or fabric. In some embodiments,display engine 2040 includes a 2D engine 2041 and a display controller2043. In some embodiments, display engine 2040 contains special purposelogic capable of operating independently of the 3D pipeline. In someembodiments, display controller 2043 couples with a display device (notshown), which may be a system integrated display device, as in a laptopcomputer, or an external display device attached via a display deviceconnector.

In some embodiments, graphics pipeline 2020 and media pipeline 2030 areconfigurable to perform operations based on multiple graphics and mediaprogramming interfaces and are not specific to any one applicationprogramming interface (API). In some embodiments, driver software forthe graphics processor translates API calls that are specific to aparticular graphics or media library into commands that can be processedby the graphics processor. In some embodiments, support is provided forthe Open Graphics Library (OpenGL), Open Computing Language (OpenCL),and/or Vulkan graphics and compute API, all from the Khronos Group. Insome embodiments, support may also be provided for the Direct3D libraryfrom the Microsoft Corporation. In some embodiments, a combination ofthese libraries may be supported. Support may also be provided for theOpen Source Computer Vision Library (OpenCV). A future API with acompatible 3D pipeline would also be supported if a mapping can be madefrom the pipeline of the future API to the pipeline of the graphicsprocessor.

Exemplary Additional Graphics Pipeline Programming

FIG. 21A is a block diagram illustrating a graphics processor commandformat 2100 according to some embodiments. FIG. 21B is a block diagramillustrating a graphics processor command sequence 2110 according to anembodiment. The solid lined boxes in FIG. 21A illustrate the componentsthat are generally included in a graphics command while the dashed linesinclude components that are optional or that are only included in asub-set of the graphics commands. The exemplary graphics processorcommand format 2100 of FIG. 21A includes data fields to identify atarget client 2102 of the command, a command operation code (opcode)2104, and the relevant data 2106 for the command. A sub-opcode 2105 anda command size 2108 are also included in some commands.

In some embodiments, client 2102 specifies the client unit of thegraphics device that processes the command data. In some embodiments, agraphics processor command parser examines the client field of eachcommand to condition the further processing of the command and route thecommand data to the appropriate client unit. In some embodiments, thegraphics processor client units include a memory interface unit, arender unit, a 2D unit, a 3D unit, and a media unit. Each client unithas a corresponding processing pipeline that processes the commands.Once the command is received by the client unit, the client unit readsthe opcode 2104 and, if present, sub-opcode 2105 to determine theoperation to perform. The client unit performs the command usinginformation in data field 2106. For some commands an explicit commandsize 2108 is expected to specify the size of the command. In someembodiments, the command parser automatically determines the size of atleast some of the commands based on the command opcode. In someembodiments commands are aligned via multiples of a double word.

The flow diagram in FIG. 21B shows an exemplary graphics processorcommand sequence 2110. In some embodiments, software or firmware of adata processing system that features an embodiment of a graphicsprocessor uses a version of the command sequence shown to set up,execute, and terminate a set of graphics operations. A sample commandsequence is shown and described for purposes of example only asembodiments are not limited to these specific commands or to thiscommand sequence. Moreover, the commands may be issued as batch ofcommands in a command sequence, such that the graphics processor willprocess the sequence of commands in at least partially concurrence.

In some embodiments, the graphics processor command sequence 2110 maybegin with a pipeline flush command 2112 to cause any active graphicspipeline to complete the currently pending commands for the pipeline. Insome embodiments, the 3D pipeline 2122 and the media pipeline 2124 donot operate concurrently. The pipeline flush is performed to cause theactive graphics pipeline to complete any pending commands. In responseto a pipeline flush, the command parser for the graphics processor willpause command processing until the active drawing engines completepending operations and the relevant read caches are invalidated.Optionally, any data in the render cache that is marked ‘dirty’ can beflushed to memory. In some embodiments, pipeline flush command 2112 canbe used for pipeline synchronization or before placing the graphicsprocessor into a low power state.

In some embodiments, a pipeline select command 2113 is used when acommand sequence requires the graphics processor to explicitly switchbetween pipelines. In some embodiments, a pipeline select command 2113is required only once within an execution context before issuingpipeline commands unless the context is to issue commands for bothpipelines. In some embodiments, a pipeline flush command 2112 isrequired immediately before a pipeline switch via the pipeline selectcommand 2113.

In some embodiments, a pipeline control command 2114 configures agraphics pipeline for operation and is used to program the 3D pipeline2122 and the media pipeline 2124. In some embodiments, pipeline controlcommand 2114 configures the pipeline state for the active pipeline. Inone embodiment, the pipeline control command 2114 is used for pipelinesynchronization and to clear data from one or more cache memories withinthe active pipeline before processing a batch of commands.

In some embodiments, return buffer state commands 2116 are used toconfigure a set of return buffers for the respective pipelines to writedata. Some pipeline operations require the allocation, selection, orconfiguration of one or more return buffers into which the operationswrite intermediate data during processing. In some embodiments, thegraphics processor also uses one or more return buffers to store outputdata and to perform cross thread communication. In some embodiments, thereturn buffer state 2116 includes selecting the size and number ofreturn buffers to use for a set of pipeline operations.

The remaining commands in the command sequence differ based on theactive pipeline for operations. Based on a pipeline determination 2120,the command sequence is tailored to the 3D pipeline 2122 beginning withthe 3D pipeline state 2130 or the media pipeline 2124 beginning at themedia pipeline state 2140.

The commands to configure the 3D pipeline state 2130 include 3D statesetting commands for vertex buffer state, vertex element state, constantcolor state, depth buffer state, and other state variables that are tobe configured before 3D primitive commands are processed. The values ofthese commands are determined at least in part based on the particular3D API in use. In some embodiments, 3D pipeline state 2130 commands arealso able to selectively disable or bypass certain pipeline elements ifthose elements will not be used.

In some embodiments, 3D primitive 2132 command is used to submit 3Dprimitives to be processed by the 3D pipeline. Commands and associatedparameters that are passed to the graphics processor via the 3Dprimitive 2132 command are forwarded to the vertex fetch function in thegraphics pipeline. The vertex fetch function uses the 3D primitive 2132command data to generate vertex data structures. The vertex datastructures are stored in one or more return buffers. In someembodiments, 3D primitive 2132 command is used to perform vertexoperations on 3D primitives via vertex shaders. To process vertexshaders, 3D pipeline 2122 dispatches shader execution threads tographics processor execution units.

In some embodiments, 3D pipeline 2122 is triggered via an execute 2134command or event. In some embodiments, a register write triggers commandexecution. In some embodiments execution is triggered via a ‘go’ or‘kick’ command in the command sequence. In one embodiment, commandexecution is triggered using a pipeline synchronization command to flushthe command sequence through the graphics pipeline. The 3D pipeline willperform geometry processing for the 3D primitives. Once operations arecomplete, the resulting geometric objects are rasterized and the pixelengine colors the resulting pixels. Additional commands to control pixelshading and pixel back end operations may also be included for thoseoperations.

In some embodiments, the graphics processor command sequence 2110follows the media pipeline 2124 path when performing media operations.In general, the specific use and manner of programming for the mediapipeline 2124 depends on the media or compute operations to beperformed. Specific media decode operations may be offloaded to themedia pipeline during media decode. In some embodiments, the mediapipeline can also be bypassed and media decode can be performed in wholeor in part using resources provided by one or more general purposeprocessing cores. In one embodiment, the media pipeline also includeselements for general-purpose graphics processor unit (GPGPU) operations,where the graphics processor is used to perform SIMD vector operationsusing computational shader programs that are not explicitly related tothe rendering of graphics primitives.

In some embodiments, media pipeline 2124 is configured in a similarmanner as the 3D pipeline 2122. A set of commands to configure the mediapipeline state 2140 are dispatched or placed into a command queue beforethe media object commands 2142. In some embodiments, commands for themedia pipeline state 2140 include data to configure the media pipelineelements that will be used to process the media objects. This includesdata to configure the video decode and video encode logic within themedia pipeline, such as encode or decode format. In some embodiments,commands for the media pipeline state 2140 also support the use of oneor more pointers to “indirect” state elements that contain a batch ofstate settings.

In some embodiments, media object commands 2142 supply pointers to mediaobjects for processing by the media pipeline. The media objects includememory buffers containing video data to be processed. In someembodiments, all media pipeline states must be valid before issuing amedia object command 2142. Once the pipeline state is configured andmedia object commands 2142 are queued, the media pipeline 2124 istriggered via an execute command 2144 or an equivalent execute event(e.g., register write). Output from media pipeline 2124 may then be postprocessed by operations provided by the 3D pipeline 2122 or the mediapipeline 2124. In some embodiments, GPGPU operations are configured andexecuted in a similar manner as media operations.

Exemplary Graphics Software Architecture

FIG. 22 illustrates exemplary graphics software architecture for a dataprocessing system 2200 according to some embodiments. In someembodiments, software architecture includes a 3D graphics application2210, an operating system 2220, and at least one processor 2230. In someembodiments, processor 2230 includes a graphics processor 2232 and oneor more general-purpose processor core(s) 2234. The graphics application2210 and operating system 2220 each execute in the system memory 2250 ofthe data processing system.

In some embodiments, 3D graphics application 2210 contains one or moreshader programs including shader instructions 2212. The shader languageinstructions may be in a high-level shader language, such as the HighLevel Shader Language (HLSL) or the OpenGL Shader Language (GLSL). Theapplication also includes executable instructions 2214 in a machinelanguage suitable for execution by the general-purpose processor core2234. The application also includes graphics objects 2216 defined byvertex data.

In some embodiments, operating system 2220 is a Microsoft® Windows®operating system from the Microsoft Corporation, a proprietary UNIX-likeoperating system, or an open source UNIX-like operating system using avariant of the Linux kernel. The operating system 2220 can support agraphics API 2222 such as the Direct3D API, the OpenGL API, or theVulkan API. When the Direct3D API is in use, the operating system 2220uses a front-end shader compiler 2224 to compile any shader instructions2212 in HLSL into a lower-level shader language. The compilation may bea just-in-time (JIT) compilation or the application can perform shaderpre-compilation. In some embodiments, high-level shaders are compiledinto low-level shaders during the compilation of the 3D graphicsapplication 2210. In some embodiments, the shader instructions 2212 areprovided in an intermediate form, such as a version of the StandardPortable Intermediate Representation (SPIR) used by the Vulkan API.

In some embodiments, user mode graphics driver 2226 contains a back-endshader compiler 2227 to convert the shader instructions 2212 into ahardware specific representation. When the OpenGL API is in use, shaderinstructions 2212 in the GLSL high-level language are passed to a usermode graphics driver 2226 for compilation. In some embodiments, usermode graphics driver 2226 uses operating system kernel mode functions2228 to communicate with a kernel mode graphics driver 2229. In someembodiments, kernel mode graphics driver 2229 communicates with graphicsprocessor 2232 to dispatch commands and instructions.

Exemplary IP Core Implementations

One or more aspects of at least one embodiment may be implemented byrepresentative code stored on a machine-readable medium which representsand/or defines logic within an integrated circuit such as a processor.For example, the machine-readable medium may include instructions whichrepresent various logic within the processor. When read by a machine,the instructions may cause the machine to fabricate the logic to performthe techniques described herein. Such representations, known as “IPcores,” are reusable units of logic for an integrated circuit that maybe stored on a tangible, machine-readable medium as a hardware modelthat describes the structure of the integrated circuit. The hardwaremodel may be supplied to various customers or manufacturing facilities,which load the hardware model on fabrication machines that manufacturethe integrated circuit. The integrated circuit may be fabricated suchthat the circuit performs operations described in association with anyof the embodiments described herein.

FIG. 23 is a block diagram illustrating an IP core development system2300 that may be used to manufacture an integrated circuit to performoperations according to an embodiment. The IP core development system2300 may be used to generate modular, re-usable designs that can beincorporated into a larger design or used to construct an entireintegrated circuit (e.g., an SOC integrated circuit). A design facility2330 can generate a software simulation 2310 of an IP core design in ahigh level programming language (e.g., C/C++). The software simulation2310 can be used to design, test, and verify the behavior of the IP coreusing a simulation model 2312. The simulation model 2312 may includefunctional, behavioral, and/or timing simulations. A register transferlevel (RTL) design 2315 can then be created or synthesized from thesimulation model 2312. The RTL design 2315 is an abstraction of thebehavior of the integrated circuit that models the flow of digitalsignals between hardware registers, including the associated logicperformed using the modeled digital signals. In addition to an RTLdesign 2315, lower-level designs at the logic level or transistor levelmay also be created, designed, or synthesized. Thus, the particulardetails of the initial design and simulation may vary.

The RTL design 2315 or equivalent may be further synthesized by thedesign facility into a hardware model 2320, which may be in a hardwaredescription language (HDL), or some other representation of physicaldesign data. The HDL may be further simulated or tested to verify the IPcore design. The IP core design can be stored for delivery to a 3^(rd)party fabrication facility 2365 using non-volatile memory 2340 (e.g.,hard disk, flash memory, or any non-volatile storage medium).Alternatively, the IP core design may be transmitted (e.g., via theInternet) over a wired connection 2350 or wireless connection 2360. Thefabrication facility 2365 may then fabricate an integrated circuit thatis based at least in part on the IP core design. The fabricatedintegrated circuit can be configured to perform operations in accordancewith at least one embodiment described herein.

Exemplary System on a Chip Integrated Circuit

FIGS. 24-26 illustrated exemplary integrated circuits and associatedgraphics processors that may be fabricated using one or more IP cores,according to various embodiments described herein. In addition to whatis illustrated, other logic and circuits may be included, includingadditional graphics processors/cores, peripheral interface controllers,or general purpose processor cores.

FIG. 24 is a block diagram illustrating an exemplary system on a chipintegrated circuit 2400 that may be fabricated using one or more IPcores, according to an embodiment. Exemplary integrated circuit 2400includes one or more application processor(s) 2405 (e.g., CPUs), atleast one graphics processor 2410, and may additionally include an imageprocessor 2415 and/or a video processor 2420, any of which may be amodular IP core from the same or multiple different design facilities.Integrated circuit 2400 includes peripheral or bus logic including a USBcontroller 2425, UART controller 2430, an SPI/SDIO controller 2435, andan I²S/I²C controller 2440. Additionally, the integrated circuit caninclude a display device 2445 coupled to one or more of ahigh-definition multimedia interface (HDMI) controller 2450 and a mobileindustry processor interface (MIPI) display interface 2455. Storage maybe provided by a flash memory subsystem 2460 including flash memory anda flash memory controller. Memory interface may be provided via a memorycontroller 2465 for access to SDRAM or SRAM memory devices. Someintegrated circuits additionally include an embedded security engine2470.

FIG. 25 is a block diagram illustrating an exemplary graphics processor2510 of a system on a chip integrated circuit that may be fabricatedusing one or more IP cores, according to an embodiment. Graphicsprocessor 2510 can be a variant of the graphics processor 2410 of FIG.24. Graphics processor 2510 includes a vertex processor 2505 and one ormore fragment processor(s) 2515A-2515N (e.g., 2515A, 2515B, 2515C,2515D, through 2515N-1, and 2515N). Graphics processor 2510 can executedifferent shader programs via separate logic, such that the vertexprocessor 2505 is optimized to execute operations for vertex shaderprograms, while the one or more fragment processor(s) 2515A-2515Nexecute fragment (e.g., pixel) shading operations for fragment or pixelshader programs. The vertex processor 2505 performs the vertexprocessing stage of the 3D graphics pipeline and generates primitivesand vertex data. The fragment processor(s) 2515A-2515N use the primitiveand vertex data generated by the vertex processor 2505 to produce aframebuffer that is displayed on a display device. In one embodiment,the fragment processor(s) 2515A-2515N are optimized to execute fragmentshader programs as provided for in the OpenGL API, which may be used toperform similar operations as a pixel shader program as provided for inthe Direct 3D API.

Graphics processor 2510 additionally includes one or more memorymanagement units (MMUs) 2520A-2520B, cache(s) 2525A-2525B, and circuitinterconnect(s) 2530A-2530B. The one or more MMU(s) 2520A-2520B providefor virtual to physical address mapping for integrated circuit 2510,including for the vertex processor 2505 and/or fragment processor(s)2515A-2515N, which may reference vertex or image/texture data stored inmemory, in addition to vertex or image/texture data stored in the one ormore cache(s) 2525A-2525B. In one embodiment the one or more MMU(s)2520A-2520B may be synchronized with other MMUs within the system,including one or more MMUs associated with the one or more applicationprocessor(s) 2405, image processor 2415, and/or video processor 2420 ofFIG. 24, such that each processor 2405-2420 can participate in a sharedor unified virtual memory system. The one or more circuitinterconnect(s) 2530A-2530B enable graphics processor 2510 to interfacewith other IP cores within the SoC, either via an internal bus of theSoC or via a direct connection, according to embodiments.

FIG. 26 is a block diagram illustrating an additional exemplary graphicsprocessor 2610 of a system on a chip integrated circuit that may befabricated using one or more IP cores, according to an embodiment.Graphics processor 2610 can be a variant of the graphics processor 2410of FIG. 24. Graphics processor 2610 includes the one or more MMU(s)2520A-2520B, caches 2525A-2525B, and circuit interconnects 2530A-2530Bof the integrated circuit 2500 of FIG. 25.

Graphics processor 2610 includes one or more shader core(s) 2615A-2615N(e.g., 2615A, 2615B, 2615C, 2615D, 2615E, 2615F, through 2615N-1, and2615N), which provides for a unified shader core architecture in which asingle core or type or core can execute all types of programmable shadercode, including shader program code to implement vertex shaders,fragment shaders, and/or compute shaders. The exact number of shadercores present can vary among embodiments and implementations.Additionally, graphics processor 2610 includes an inter-core taskmanager 2605, which acts as a thread dispatcher to dispatch executionthreads to one or more shader cores 2615A-2615N and a tiling unit 2618to accelerate tiling operations for tile-based rendering, in whichrendering operations for a scene are subdivided in image space, forexample to exploit local spatial coherence within a scene or to optimizeuse of internal caches.

The following clauses and/or examples pertain to specific embodiments orexamples thereof. Specifics in the examples may be used anywhere in oneor more embodiments. The various features of the different embodimentsor examples may be variously combined with some features included andothers excluded to suit a variety of different applications. Examplesmay include subject matter such as a method, means for performing actsof the method, at least one machine-readable medium includinginstructions that, when performed by a machine cause the machine toperform acts of the method, or of an apparatus or system according toembodiments and examples described herein. Various components can be ameans for performing the operations or functions described.

One embodiment provides for a parallel processor comprising a processingarray within the parallel processor, the processing array includingmultiple compute blocks, each compute block including multipleprocessing clusters configured for parallel operation, and each of themultiple compute blocks is independently preemptable. In one embodimentthe parallel processor is a GPGPU configured for SIMT execution. In oneembodiment the parallel processor includes a scheduler module toschedule a workload to the multiple compute blocks. The scheduler modulecan be an embedded microcontroller. In one embodiment the multiplecompute blocks include a first compute block and a second compute block.The first compute block can be configured to preempt a first work groupof the workload while the second compute block is to execute a secondwork group of the workload. In one embodiment the processing array isconfigured to address memory via a virtual address mapping and isconfigured to support page faulting for the virtual address mapping. Thefirst compute block can be configured to detect that a first work grouphas a number of unhandled page faults over a threshold, halt executionof the first work group, and save a context state for the first workgroup. In one embodiment the parallel processor additionally includes acontext save memory to store a context state for each of the multiplecompute blocks and the first compute block is to save the context statefor the first work group to the context save memory. In one embodimentthe context save memory is dedicated to the first compute block.

In one embodiment the first compute block and a second compute blockshare a set of shared assets within the processing array. The set ofshared assets can include a texture unit, a texture sampler, and a cachememory. The set of shared assets can also include an address generationunit and an address mapping unit. In one embodiment the context statefor the first work group includes context state for the set of sharedassets.

One embodiment provides for a method of workload management on aparallel processor, the method comprising, in response to receiving anotice that a number of page faults associated with a first work groupon a first compute block within the parallel processor has exceeded athreshold, placing the first compute block into a preemption state whenpage fault preemption is enabled for the context associated with thefirst work group. The method additionally includes determining if afirst pending workgroup is available for execution on the first computeblock, preempting the first work group on the first compute block whenthe first pending workgroup is available for execution on the firstcompute block, and executing a second work group on a second computeblock within the parallel processor while preempting the first workgroup, wherein the first compute block and the second compute block eachinclude multiple processing clusters, each of the multiple processingclusters including multiple processing units. In one embodiment themethod additionally includes enabling page fault preemption for thecontext associated with the first work group when an average page faultlatency for the context is above a high-watermark threshold anddisabling page fault preemption for the context when the average pagefault latency for the context is below a low-watermark threshold. In oneembodiment, placing the first compute block into the preemption stateincludes saving a hardware context state associated with the firstcompute block to a context save memory and saving the hardware contextstate associated with the first compute block to the context save memoryincludes saving a context state associated with at least the first workgroup.

One embodiment provides for a method of workload management on ageneral-purpose graphics processing unit (GPGPU), the method comprisingcompiling source code for execution on the GPGPU to generate compiledsource code. While compiling the source code, a compiler can generatemetadata associated with one or more instructions of the compiled sourcecode, where the metadata is to indicate a size of a context save statewhen preempting execution at the one or more instructions. In oneembodiment the metadata includes a preemption hint that indicates anregister file usage or a pending change in the register file usage inthe next set of instructions.

The embodiments described herein refer to specific configurations ofhardware, such as application specific integrated circuits (ASICs),configured to perform certain operations or having a predeterminedfunctionality. Such electronic devices typically include a set of one ormore processors coupled to one or more other components, such as one ormore storage devices (non-transitory machine-readable storage media),user input/output devices (e.g., a keyboard, a touchscreen, and/or adisplay), and network connections. The coupling of the set of processorsand other components is typically through one or more busses and bridges(also termed as bus controllers). The storage device and signalscarrying the network traffic respectively represent one or moremachine-readable storage media and machine-readable communication media.Thus, the storage devices of a given electronic device typically storecode and/or data for execution on the set of one or more processors ofthat electronic device.

Of course, one or more parts of an embodiment may be implemented usingdifferent combinations of software, firmware, and/or hardware.Throughout this detailed description, for the purposes of explanation,numerous specific details were set forth in order to provide a thoroughunderstanding of the present invention. It will be apparent, however, toone skilled in the art that the embodiments may be practiced withoutsome of these specific details. In certain instances, well-knownstructures and functions were not described in elaborate detail to avoidobscuring the inventive subject matter of the embodiments. Accordingly,the scope and spirit of the invention should be judged in terms of theclaims that follow.

What is claimed is:
 1. A parallel processor comprising: a processingarray within the parallel processor, the processing array includingmultiple compute blocks, each compute block including multipleprocessing clusters to perform parallel operations, the processing arrayto address memory via a virtual address mapping and support pagefaulting for the virtual address mapping, wherein each of the multiplecompute blocks is independently preemptable; and a scheduler to schedulea workload to the multiple compute blocks, wherein the scheduler is totrack an average latency to resolve a page fault.
 2. The parallelprocessor as in claim 1, wherein the parallel processor is ageneral-purpose graphics processing unit (GPGPU).
 3. The parallelprocessor as in claim 2, wherein the parallel processor is a singleinstruction multiple thread (SIMT) processor.
 4. The parallel processoras in claim 1, wherein the scheduler is an embedded microcontroller. 5.The parallel processor as in claim 1, wherein the multiple computeblocks include a first compute block and a second compute block.
 6. Theparallel processor as in claim 5, wherein the first compute block is topreempt a first work group of the workload while the second computeblock is to execute a second work group of the workload.
 7. The parallelprocessor as in claim 5, wherein the first compute block is to detectthat a first work group of the workload has a number of unhandled pagefaults over a threshold, halt execution of the first work group, andsave a context state for the first work group.
 8. The parallel processoras in claim 7, additionally including a context save memory to store thecontext state for each of the multiple compute blocks, wherein the firstcompute block is to save the context state for the first work group tothe context save memory.
 9. The parallel processor as in claim 8,wherein the first compute block is to save the context state for thefirst work group to a region of the context save memory that isdedicated to the first compute block.
 10. A data processing systemcomprising: a memory; a parallel processor coupled with the memory, theparallel processor including a processing array, wherein the processingarray is to address memory via a virtual address mapping and supportpage faulting for the virtual address mapping, the processing arrayincluding: multiple compute blocks including multiple processingclusters to perform parallel operations, wherein each of the multiplecompute blocks is independently preemptable; and a scheduler to schedulea workload to the multiple compute blocks, wherein the scheduler is totrack an average latency to resolve a page fault.
 11. The dataprocessing system as in claim 10, wherein the parallel processor is ageneral-purpose graphics processing unit (GPGPU).
 12. The dataprocessing system as in claim 11, wherein the parallel processor is asingle instruction multiple thread (SIMT) processor.
 13. The dataprocessing system as in claim 12, wherein scheduler module is anembedded microcontroller.
 14. The data processing system as in claim 10,wherein the multiple compute blocks include a first compute block and asecond compute block.
 15. The data processing system as in claim 14,wherein the first compute block is to preempt a first work group of theworkload while the second compute block is to execute a second workgroup of the workload.
 16. The data processing system as in claim 10,wherein a first compute block of the multiple compute blocks is todetect that a first work group has a number of unhandled page faultsover a threshold, halt execution of the first work group, and save acontext state for the first work group.
 17. The data processing systemas in claim 16, additionally including a context save memory to storethe context state for each of the multiple compute blocks, wherein thefirst compute block is to save the context state for the first workgroup to the context save memory.
 18. The data processing system as inclaim 17, wherein the first compute block is to save the context statefor the first work group to a region of the context save memory that isdedicated to the first compute block.
 19. A method implemented on aparallel processor, the method comprising: generating virtual addressmapping for a processing array within the parallel processor, theprocessing array to address memory via the virtual address mapping andsupport page faulting for the virtual address mapping, wherein theprocessing array includes multiple compute blocks, each of the multiplecompute blocks is independently preemptable, and each compute blockincludes multiple processing clusters to perform parallel operations;scheduling a workload to one or more of the multiple compute blocks; andtracking an average latency to resolve a page fault for the workload.20. The method as in claim 19, additionally comprising: detecting that afirst work group of the workload has a number of unhandled page faultsover a threshold; halting execution of the first work group; and savinga context state for the first work group.